Add a small JS parser to ease the building of ASTs

sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart b/sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart
index 745b5d4b89761aa1d1e8221358529975ccb48e78..70456282398977bdafff737589ffeeb03b4c8775 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart
@@ -98,17 +98,16 @@ class ConstantReferenceEmitter implements ConstantVisitor<jsAst.Expression> {
   jsAst.Expression visitTrue(TrueConstant constant) {
     if (compiler.enableMinification) {
       // Use !0 for true.
-      return new jsAst.Prefix("!", new jsAst.LiteralNumber("0"));
+      return js["!0"];
     } else {
       return new jsAst.LiteralBool(true);
     }
-
   }
 
   jsAst.Expression visitFalse(FalseConstant constant) {
     if (compiler.enableMinification) {
       // Use !1 for false.
-      return new jsAst.Prefix("!", new jsAst.LiteralNumber("1"));
+      return js["!1"];
     } else {
       return new jsAst.LiteralBool(false);
     }