Improve `for..of` control flow tests

- Expand ambiguous assertion messages and assert execution paths more
  finely.
- Improve variable names in `for..of` tests
  While the object created by a GeneratorFunction may be considered an
  "iterable", it is being used as an iterator in these tests. Naming the
  variable according to the way it is used improves the readability of
  the test body.
- Add 'features' attribute to test frontmatter
- Move tests
- Introduce additional `for..of` control flow tests

test/language/statements/for-of/yield-from-try.js

+// Copyright (C) 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 13.6.4.13
+description: >
+    Control flow during body evaluation should honor `yield` statements within
+    `try` blocks.
+features: [generators]
+---*/
+
+function* values() {
+  yield 1;
+  yield 1;
+}
+var dataIterator = values();
+var controlIterator = (function*() {
+  for (var x of dataIterator) {
+    try {
+      i++;
+      yield;
+      j++;
+    } catch (err) {}
+    k++;
+  }
+
+  l++;
+})();
+var i = 0;
+var j = 0;
+var k = 0;
+var l = 0;
+
+controlIterator.next();
+assert.sameValue(i, 1, 'First iteration: pre-yield');
+assert.sameValue(j, 0, 'First iteration: post-yield');
+assert.sameValue(k, 0, 'First iteration: post-try');
+assert.sameValue(l, 0, 'First iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Second iteration: pre-yield');
+assert.sameValue(j, 1, 'Second iteration: post-yield');
+assert.sameValue(k, 1, 'Second iteration: post-try');
+assert.sameValue(l, 0, 'Second iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Third iteration: pre-yield');
+assert.sameValue(j, 2, 'Third iteration: post-yield');
+assert.sameValue(k, 2, 'Third iteration: post-try');
+assert.sameValue(l, 1, 'Third iteration: post-for-of');

test/language/statements/for-of/yield-star-from-catch.js

+// Copyright (C) 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 13.6.4.13
+description: >
+    Control flow during body evaluation should honor `yield *` statements
+    within the `catch` block of `try` statements.
+features: [generators]
+---*/
+
+function* values() {
+  yield 1;
+  yield 1;
+}
+var dataIterator = values();
+var controlIterator = (function*() {
+  for (var x of dataIterator) {
+    try {
+      throw new Error();
+      $ERROR('This code is unreachable.');
+    } catch (err) {
+      i++;
+      yield * values();
+      j++;
+    }
+    k++;
+  }
+
+  l++;
+})();
+var i = 0;
+var j = 0;
+var k = 0;
+var l = 0;
+
+controlIterator.next();
+assert.sameValue(i, 1, 'First iteration: pre-yield');
+assert.sameValue(j, 0, 'First iteration: post-yield');
+assert.sameValue(k, 0, 'First iteration: post-try');
+assert.sameValue(l, 0, 'First iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 1, 'Second iteration: pre-yield');
+assert.sameValue(j, 0, 'Second iteration: post-yield');
+assert.sameValue(k, 0, 'Second iteration: post-try');
+assert.sameValue(l, 0, 'Second iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Third iteration: pre-yield');
+assert.sameValue(j, 1, 'Third iteration: post-yield');
+assert.sameValue(k, 1, 'Third iteration: post-try');
+assert.sameValue(l, 0, 'Third iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Fourth iteration: pre-yield');
+assert.sameValue(j, 1, 'Fourth iteration: post-yield');
+assert.sameValue(k, 1, 'Fourth iteration: post-try');
+assert.sameValue(l, 0, 'Fourth iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Fifth iteration: pre-yield');
+assert.sameValue(j, 2, 'Fifth iteration: post-yield');
+assert.sameValue(k, 2, 'Fifth iteration: post-try');
+assert.sameValue(l, 1, 'Fifth iteration: post-for-of');

test/language/statements/for-of/yield-star-from-finally.js

+// Copyright (C) 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 13.6.4.13
+description: >
+    Control flow during body evaluation should honor `yield *` statements
+    within the `finally` block of `try` statements.
+features: [generators]
+---*/
+
+function* values() {
+  yield 1;
+  yield 1;
+}
+var dataIterator = values();
+var controlIterator = (function*() {
+  for (var x of dataIterator) {
+    try {
+    } finally {
+      i++;
+      yield * values();
+      j++;
+    }
+    k++;
+  }
+
+  l++;
+})();
+var i = 0;
+var j = 0;
+var k = 0;
+var l = 0;
+
+controlIterator.next();
+assert.sameValue(i, 1, 'First iteration: pre-yield');
+assert.sameValue(j, 0, 'First iteration: post-yield');
+assert.sameValue(k, 0, 'First iteration: post-try');
+assert.sameValue(l, 0, 'First iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 1, 'Second iteration: pre-yield');
+assert.sameValue(j, 0, 'Second iteration: post-yield');
+assert.sameValue(k, 0, 'Second iteration: post-try');
+assert.sameValue(l, 0, 'Second iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Third iteration: pre-yield');
+assert.sameValue(j, 1, 'Third iteration: post-yield');
+assert.sameValue(k, 1, 'Third iteration: post-try');
+assert.sameValue(l, 0, 'Third iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Fourth iteration: pre-yield');
+assert.sameValue(j, 1, 'Fourth iteration: post-yield');
+assert.sameValue(k, 1, 'Fourth iteration: post-try');
+assert.sameValue(l, 0, 'Fourth iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Fifth iteration: pre-yield');
+assert.sameValue(j, 2, 'Fifth iteration: post-yield');
+assert.sameValue(k, 2, 'Fifth iteration: post-try');
+assert.sameValue(l, 1, 'Fifth iteration: post-for-of');

test/language/statements/for-of/yield-star-from-try.js

+// Copyright (C) 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 13.6.4.13
+description: >
+    Control flow during body evaluation should honor `yield *` statements
+    within `try` blocks.
+features: [generators]
+---*/
+
+function* values() {
+  yield 1;
+  yield 1;
+}
+var dataIterator = values();
+var controlIterator = (function*() {
+  for (var x of dataIterator) {
+    try {
+      i++;
+      yield * values();
+      j++;
+    } catch (err) {}
+    k++;
+  }
+
+  l++;
+})();
+var i = 0;
+var j = 0;
+var k = 0;
+var l = 0;
+
+controlIterator.next();
+assert.sameValue(i, 1, 'First iteration: pre-yield');
+assert.sameValue(j, 0, 'First iteration: post-yield');
+assert.sameValue(k, 0, 'First iteration: post-try');
+assert.sameValue(l, 0, 'First iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 1, 'Second iteration: pre-yield');
+assert.sameValue(j, 0, 'Second iteration: post-yield');
+assert.sameValue(k, 0, 'Second iteration: post-try');
+assert.sameValue(l, 0, 'Second iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Third iteration: pre-yield');
+assert.sameValue(j, 1, 'Third iteration: post-yield');
+assert.sameValue(k, 1, 'Third iteration: post-try');
+assert.sameValue(l, 0, 'Third iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Fourth iteration: pre-yield');
+assert.sameValue(j, 1, 'Fourth iteration: post-yield');
+assert.sameValue(k, 1, 'Fourth iteration: post-try');
+assert.sameValue(l, 0, 'Fourth iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Fifth iteration: pre-yield');
+assert.sameValue(j, 2, 'Fifth iteration: post-yield');
+assert.sameValue(k, 2, 'Fifth iteration: post-try');
+assert.sameValue(l, 1, 'Fifth iteration: post-for-of');

test/language/statements/for-of/yield-star.js

+// Copyright (C) 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 13.6.4.13
+description: >
+    Control flow during body evaluation should honor `yield *` statements.
+features: [generators]
+---*/
+
+function* values() {
+  yield 1;
+  yield 1;
+}
+var dataIterator = values();
+var controlIterator = (function*() {
+  for (var x of dataIterator) {
+    i++;
+    yield * values();
+    j++;
+  }
+
+  k++;
+})();
+var i = 0;
+var j = 0;
+var k = 0;
+
+controlIterator.next();
+assert.sameValue(i, 1, 'First iteration: pre-yield');
+assert.sameValue(j, 0, 'First iteration: post-yield');
+assert.sameValue(k, 0, 'First iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 1, 'Second iteration: pre-yield');
+assert.sameValue(j, 0, 'Second iteration: post-yield');
+assert.sameValue(k, 0, 'Second iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Third iteration: pre-yield');
+assert.sameValue(j, 1, 'Third iteration: post-yield');
+assert.sameValue(k, 0, 'Third iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Fourth iteration: pre-yield');
+assert.sameValue(j, 1, 'Fourth iteration: post-yield');
+assert.sameValue(k, 0, 'Fourth iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Fifth iteration: pre-yield');
+assert.sameValue(j, 2, 'Fifth iteration: post-yield');
+assert.sameValue(k, 1, 'Fifth iteration: post-for-of');

test/language/statements/for-of/yield.js

+// Copyright (C) 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 13.6.4.13
+description: >
+    Control flow during body evaluation should honor `yield` statements.
+features: [generators]
+---*/
+
+function* values() {
+  yield 1;
+  yield 1;
+}
+var dataIterator = values();
+var controlIterator = (function*() {
+  for (var x of dataIterator) {
+    i++;
+    yield;
+    j++;
+  }
+
+  k++;
+})();
+var i = 0;
+var j = 0;
+var k = 0;
+
+controlIterator.next();
+assert.sameValue(i, 1, 'First iteration: pre-yield');
+assert.sameValue(j, 0, 'First iteration: post-yield');
+assert.sameValue(k, 0, 'First iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Second iteration: pre-yield');
+assert.sameValue(j, 1, 'Second iteration: post-yield');
+assert.sameValue(k, 0, 'Second iteration: post-for-of');
+
+controlIterator.next();
+assert.sameValue(i, 2, 'Third iteration: pre-yield');
+assert.sameValue(j, 2, 'Third iteration: post-yield');
+assert.sameValue(k, 1, 'Third iteration: post-for-of');