Add parsing for ambient declarations

test/mjsunit/harmony/typesystem/variable-declarations.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --harmony-types
 
 
 load("test/mjsunit/harmony/typesystem/typegen.js");
 debug = true;
 
@@ skipping 33 matching lines @@
       t => keyword + " [x, y, ...rest] : (" + t + ")[] = [];"
     ]),
     new TestGen(1, InvalidTupleTypes, [
       keyword != "const" && (t => keyword + " [x,, z] : " + t + ";"),
       t => keyword + " [x,, z] : " + t + " = [undefined,, undefined];"
     ]),
     new TestGen(1, InvalidObjectTypes, [
       keyword != "const" && (t => keyword + " {a: x, b: y} : " + t + ";"),
       t => keyword + " {a: x, b: y} : " + t + " = {a: 17, b: 42};"
     ]),
-    "var [x, y]: number[];",
-    "var {a: x, b: y}: {a: number, b: string};",
-    "let [x, y]: number[];",
-    "let {a: x, b: y}: {a: number, b: string};",
-    "const x: number;",
-    "const [x, y]: [number, string];",
-    "const {a: x, b: y}: {a: number, b: string};"
+    keyword + " [x, y]: number[];",
+    keyword + " {a: x, b: y}: {a: number, b: string};",
+    keyword == "const" && keyword + " x: number;"
   ]);
 }
 
 (function TestVariableDeclarations(size) {
   Test(size, [
     new TestGen(1, ValidVariableDeclarations, [CheckValid], "var"),
     new TestGen(1, ValidVariableDeclarations, [CheckValid], "let"),
     new TestGen(1, ValidVariableDeclarations, [CheckValid], "const"),
     new TestGen(1, InvalidVariableDeclarations, [CheckInvalid], "var"),
     new TestGen(1, InvalidVariableDeclarations, [CheckInvalid], "let"),
     new TestGen(1, InvalidVariableDeclarations, [CheckInvalid], "const")
   ]);
 })(test_size);