Add test templates for spread in array initializer

Formulate templates for the SpreadElement in an array initializer in
order to conform to existing pattern.

src/spread/default/array.template

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+path: language/expressions/array/spread-
+name: Array initializer
+esid: sec-runtime-semantics-arrayaccumulation
+es6id: 12.2.5.2
+info: |
+  SpreadElement : ...AssignmentExpression
+
+  1. Let spreadRef be the result of evaluating AssignmentExpression.
+  2. Let spreadObj be ? GetValue(spreadRef).
+  3. Let iterator be ? GetIterator(spreadObj).
+  4. Repeat
+     a. Let next be ? IteratorStep(iterator).
+     b. If next is false, return nextIndex.
+     c. Let nextValue be ? IteratorValue(next).
+     d. Let status be CreateDataProperty(array, ToString(ToUint32(nextIndex)),
+        nextValue).
+     e. Assert: status is true.
+     f. Let nextIndex be nextIndex + 1.
+---*/
+
+var callCount = 0;
+
+(function(/*{ params }*/) {
+  /*{ body }*/
+  callCount += 1;
+}.apply(null, [/*{ args }*/]));
+
+assert.sameValue(callCount, 1);

src/spread/error/array.template

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+path: language/expressions/array/spread-err-
+name: Array initializer
+esid: sec-runtime-semantics-arrayaccumulation
+es6id: 12.2.5.2
+info: |
+  SpreadElement : ...AssignmentExpression
+
+  1. Let spreadRef be the result of evaluating AssignmentExpression.
+  2. Let spreadObj be ? GetValue(spreadRef).
+  3. Let iterator be ? GetIterator(spreadObj).
+  4. Repeat
+     a. Let next be ? IteratorStep(iterator).
+     b. If next is false, return nextIndex.
+     c. Let nextValue be ? IteratorValue(next).
+     d. Let status be CreateDataProperty(array, ToString(ToUint32(nextIndex)),
+        nextValue).
+     e. Assert: status is true.
+     f. Let nextIndex be nextIndex + 1.
+---*/
+
+assert.throws(/*{ error }*/, function() {
+  [/*{ args }*/];
+});