Add tests for early errors in module syntax

Introduce the `module` flag to unambiguously identify tests that are
intended to be interpreted as module code.

CONTRIBUTING.md

@@ -115,6 +115,8 @@ This tag is for boolean properties associated with the test.
 
 - **`onlyStrict`** - only run the test in strict mode (*not supported by the browser runner*)
 - **`noStrict`** - only run the test in "sloppy" mode
+- **`module`** - interpret the source text as [module
+  code](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-modules)
 
 #### features
 **features**: [list]

test/language/import/dup-bound-names.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if the BoundNames of ImportDeclaration contains any
+    duplicate entries.
+flags: [module]
+negative: SyntaxError
+---*/
+
+import { x, y as x } from 'z';

test/language/module-code/dup-export-decl.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if the ExportedNames of ModuleItemList contains any
+    duplicate entries.
+flags: [module]
+negative: SyntaxError
+---*/
+
+export function f() {}
+export function *f() {}

test/language/module-code/dup-export-dflt.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if the ExportedNames of ModuleItemList contains any
+    duplicate entries.
+flags: [module]
+negative: SyntaxError
+---*/
+
+export default var x = null;
+export default var x = null;

test/language/module-code/dup-export-id-as.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if the ExportedNames of ModuleItemList contains any
+    duplicate entries.
+flags: [module]
+negative: SyntaxError
+---*/
+
+var x, y;
+export { x as z };
+export { y as z };

test/language/module-code/dup-export-id.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if the ExportedNames of ModuleItemList contains any
+    duplicate entries.
+flags: [module]
+negative: SyntaxError
+---*/
+
+var x;
+export { x };
+export { x };

test/language/module-code/dup-lables.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if ContainsDuplicateLabels of ModuleItemList with
+    argument « » is true.
+flags: [module]
+negative: SyntaxError
+---*/
+
+label: {
+  label: 0;
+}

test/language/module-code/dup-lex.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 10.2.1
+description: >
+    It is a Syntax Error if the LexicallyDeclaredNames of ModuleItemList
+    contains any duplicate entries.
+flags: [module]
+features: [let, const]
+negative: SyntaxError
+---*/
+
+let x;
+const x;

test/language/module-code/export-unresolvable.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if any element of the ExportedBindings of
+    ModuleItemList does not also occur in either the VarDeclaredNames of
+    ModuleItemList, or the LexicallyDeclaredNames of ModuleItemList.
+flags: [module]
+negative: SyntaxError
+---*/
+
+export { unresolvable };

test/language/module-code/import-as-stmt-list-item.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2
+description: >
+    An ImportDeclaration is not a valid StatementListItem and is therefore
+    restricted from appearing within statements in a ModuleBody.
+flags: [module]
+negative: SyntaxError
+---*/
+
+{
+  import { x } from 'y';
+}

test/language/module-code/lex-and-var.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 10.2.1
+description: >
+    It is a Syntax Error if any element of the LexicallyDeclaredNames of
+    ModuleItemList also occurs in the VarDeclaredNames of ModuleItemList.
+flags: [module]
+features: [let]
+---*/
+
+let x;
+var x;

test/language/module-code/new-target.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if ModuleItemList Contains NewTarget
+flags: [module]
+negative: SyntaxError
+---*/
+
+new.target;

test/language/module-code/super.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if ModuleItemList Contains super.
+flags: [module]
+negative: SyntaxError
+---*/
+
+super;

test/language/module-code/undef-break.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if ContainsUndefinedBreakTarget of ModuleItemList with
+    argument « » is true.
+flags: [module]
+negative: SyntaxError
+---*/
+
+while (false) {
+  break undef;
+}

test/language/module-code/undef-continue.js

+// Copyright (C) Copyright 2015 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 15.2.1.1
+description: >
+    It is a Syntax Error if ContainsUndefinedContinueTarget of ModuleItemList
+    with arguments « » and « » is true.
+flags: [module]
+negative: SyntaxError
+---*/
+
+while (false) {
+  continue undef;
+}