dart2js: Support const symbols in the startup emitter.

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

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js.js_emitter.startup_emitter.model_emitter;
 
 /// The name of the property that stores the tear-off getter on a static
 /// function.
 ///
 /// This property is only used when isolates are used.
@@ skipping 1109 matching lines @@
           o[fieldNames[i]] = fields[i];
         }
         return o;
       }''');
       globals.add(new js.Property(js.string(INITIALIZE_EMPTY_INSTANCE),
                                   initializeEmptyInstanceFunction));
     }
 
     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());
 
     globals.addAll(emitMetadata(program));
 
     if (program.needsNativeSupport) {
       globals.add(new js.Property(js.string(INTERCEPTORS_BY_TAG),
           new js.LiteralNull()));
       globals.add(new js.Property(js.string(LEAF_TAGS),
           new js.LiteralNull()));
@@ skipping 63 matching lines @@
     }
     statements.add(js.js.statement("setOrUpdateInterceptorsByTag(#);",
         js.objectLiteral(interceptorsByTag)));
     statements.add(js.js.statement("setOrUpdateLeafTags(#);",
         js.objectLiteral(leafTags)));
     statements.add(subclassAssignment);
 
     return new js.Block(statements);
   }
 }