Use JavaScript runtime semantics when constant folding.

lib/compiler/implementation/compiler.dart

Index: lib/compiler/implementation/compiler.dart
diff --git a/lib/compiler/implementation/compiler.dart b/lib/compiler/implementation/compiler.dart
index bf51eb7a1c4a8ee12d839c316677aecbf2256d27..554e59592e5cdab909f2375fb4354bba28c69022 100644
--- a/lib/compiler/implementation/compiler.dart
+++ b/lib/compiler/implementation/compiler.dart
@@ -154,14 +154,18 @@ class Compiler implements DiagnosticListener {
   Compiler([this.tracer = const Tracer(),
             this.enableTypeAssertions = false,
             this.enableUserAssertions = false,
-            bool emitJavascript = true,
+            bool emitJavaScript = true,
             validateUnparse = false,
             generateSourceMap = true])
       : libraries = new Map<String, LibraryElement>(),
         world = new World(),
         progress = new Stopwatch.start() {
     namer = new Namer(this);
-    constantHandler = new ConstantHandler(this);
+    constantHandler =
+        new ConstantHandler(this,
+                            emitJavaScript
+                            ? const JavaScriptFoldingOperations()
+                            : const DartFoldingOperations());
     scanner = new ScannerTask(this);
     dietParser = new DietParserTask(this);
     parser = new ParserTask(this);
@@ -171,7 +175,7 @@ class Compiler implements DiagnosticListener {
     closureToClassMapper = new closureMapping.ClosureTask(this);
     checker = new TypeCheckerTask(this);
     typesTask = new ti.TypesTask(this);
-    backend = emitJavascript ?
+    backend = emitJavaScript ?
         new js_backend.JavaScriptBackend(this, generateSourceMap) :
         new dart_backend.DartBackend(this, validateUnparse);
     enqueuer = new EnqueueTask(this);