dart2js: Implement frequency based naming.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 88368dd5bfc42c99f764193586f22810a87e7e9c..0a9b92cc269d7bfc2468996026c857a4bdfd489b 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -699,6 +699,8 @@ abstract class Compiler implements DiagnosticListener {
 
   final bool enableMinification;
 
+  final bool useFrequencyNamer;
+
   /// When `true` emits URIs in the reflection metadata.
   final bool preserveUris;
 
@@ -1042,6 +1044,7 @@ abstract class Compiler implements DiagnosticListener {
             bool analyzeSignaturesOnly: false,
             this.preserveComments: false,
             this.useCpsIr: false,
+            this.useFrequencyNamer: false,
             this.verbose: false,
             this.sourceMapUri: null,
             this.outputUri: null,