dart2js: Support const symbols in the startup emitter.

pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart b/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
index 0c1ef57b1e19ca9ce3d9e42c133917b6a89c651c..1ae6d417c2301834250b65e527a418e92f34ef0a 100644
--- a/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
@@ -1127,10 +1127,16 @@ class FragmentEmitter {
 
     globals.add(emitMangledGlobalNames());
 
-    // The [MANGLED_NAMES] table is only relevant for reflection.
-    // TODO(floitsch): verify that this is correct.
-    globals.add(new js.Property(js.string(MANGLED_NAMES),
-                                new js.ObjectInitializer([])));
+    // The [MANGLED_NAMES] table must contain the mapping for const symbols.
+    // Otherwise, it is only relevant for reflection.

[Siggi Cherem (dart-lang), 2015/07/23 18:09:50]

I assume that by reflection here you also mean Function.apply (since this
emitter doesn't support dart:mirrors), correct?

[floitsch, 2015/07/29 18:08:37]

Rewrote comment: Without const symbols, the table is only relevant for
reflection.

It's not needed for Function.apply.

[Siggi Cherem (dart-lang), 2015/07/30 16:44:02]

But this emitter doesn't support dart:mirrors, right? So if there are no const
symbols, is it used?

[floitsch, 2015/08/03 15:56:06]

It's unused. Updated comment.

+    List<js.Property> mangledNamesProperties = <js.Property>[];
+    program.symbolsMap.forEach((js.Name mangledName, String unmangledName) {
+      mangledNamesProperties.add(
+          new js.Property(mangledName, js.string(unmangledName)));
+    });
+    globals.add(new js.Property(
+        js.string(MANGLED_NAMES),
+        new js.ObjectInitializer(mangledNamesProperties)));
 
     globals.add(emitGetTypeFromName());