dart2js: Implement frequency based naming.

pkg/compiler/lib/src/js_backend/field_naming_mixin.dart

Index: pkg/compiler/lib/src/js_backend/field_naming_mixin.dart
diff --git a/pkg/compiler/lib/src/js_backend/field_naming_mixin.dart b/pkg/compiler/lib/src/js_backend/field_naming_mixin.dart
index 61383b92f79061dd0ec85957a729acfad1abe8e6..707e7e7636929fe89ff84514e6d5a3e390f5bd20 100644
--- a/pkg/compiler/lib/src/js_backend/field_naming_mixin.dart
+++ b/pkg/compiler/lib/src/js_backend/field_naming_mixin.dart
@@ -44,7 +44,7 @@ abstract class _MinifiedFieldNamer implements Namer {
  * hierarchy is encoded using instances of [_FieldNamingScope].
  */
 class _FieldNamingRegistry {
-  final MinifyNamer namer;
+  final Namer namer;
 
   final Map<Entity, _FieldNamingScope> scopes =
       new Map<Entity, _FieldNamingScope>();
@@ -71,14 +71,13 @@ class _FieldNamingRegistry {
       // existing properties on JS objects (see [_reservedNativeProperties]).
       // However, some of them are really short and safe to use for fields.
       // Thus, we shortcut the namer to use those first.
-      assert(index == nameStore.length + 1);
+      assert(index == nameStore.length);

[herhut, 2015/06/30 16:33:26]

this is a back-ported fix from a later revision...

       if (index < MinifyNamer._reservedNativeProperties.length &&
           MinifyNamer._reservedNativeProperties[index].length <= 2) {
         nameStore.add(
             new StringBackedName(MinifyNamer._reservedNativeProperties[index]));
       } else {
-        nameStore.add(namer.getFreshName("field$index", namer.usedInstanceNames,
-            namer.suggestedInstanceNames));
+        nameStore.add(namer.getFreshName(NamingScope.instance, "field$index"));
       }
     }