dart2js: Use frequency of occurence to sort metadata indices.

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

 // Copyright (c) 2011, 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 js_backend;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  *
  * Names are generated through three stages:
@@ skipping 1513 matching lines @@
   }
 
   @override
   void visitInterceptor(InterceptorConstantValue constant, [_]) {
     addRoot(constant.dispatchedType.element.name);
     add('methods');
   }
 
   @override
   void visitDummy(DummyConstantValue constant, [_]) {
-    add('dummy_receiver');
+    switch (constant.kind) {
+      case DummyConstantKinds.dummyReceiver:
+        add('dummy_receiver');
+        break;
+      case DummyConstantKinds.typeVariableReference:
+        add('type_variable_reference');
+        break;
+      default:
+        compiler.internalError(compiler.currentElement,
+                               "Unexpected DummyConstantValue");
+    }
   }
 
   @override
   void visitDeferred(DeferredConstantValue constant, [_]) {
     addRoot('Deferred');
   }
 }
 
 /**
  * Generates canonical hash values for [ConstantValue]s.
@@ skipping 82 matching lines @@
   }
 
   @override
   int visitInterceptor(InterceptorConstantValue constant, [_]) {
     String typeName = constant.dispatchedType.element.name;
     return _hashString(5, typeName);
   }
 
   @override
   visitDummy(DummyConstantValue constant, [_]) {
-    compiler.internalError(NO_LOCATION_SPANNABLE,
-        'DummyReceiverConstant should never be named and never be subconstant');
+    switch (constant.kind) {
+      case DummyConstantKinds.typeVariableReference:
+        return constant.payload.hashCode;
+      default:
+        compiler.internalError(NO_LOCATION_SPANNABLE,
+                               'DummyConstantValue should never be named and '
+                               'never be subconstant');
+        return null;
+    }
   }
 
   @override
   int visitDeferred(DeferredConstantValue constant, [_]) {
     int hash = constant.prefix.hashCode;
     return _combine(hash, _visit(constant.referenced));
   }
 
   int _hashString(int hash, String s) {
     int length = s.length;
@@ skipping 113 matching lines @@
         if (!first) {
           sb.write('_');
         }
         sb.write('_');
         visit(parameter);
         first = true;
       }
     }
   }
 }