dart2js: Implement frequency based naming.

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

 // Copyright (c) 2012, 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;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 658 matching lines @@
 
   bool isForeign(Element element) => element.library == foreignLibrary;
 
   bool isBackendLibrary(LibraryElement library) {
     return library == interceptorsLibrary ||
            library == jsHelperLibrary;
   }
 
   static Namer determineNamer(Compiler compiler) {
     return compiler.enableMinification ?
-        new MinifyNamer(compiler) :
+        compiler.useFrequencyNamer ?
+            new FrequencyBasedNamer(compiler) :
+            new MinifyNamer(compiler) :
         new Namer(compiler);
   }
 
   bool usedByBackend(Element element) {
     if (element.isParameter
         || element.isInitializingFormal
         || element.isField) {
       if (usedByBackend(element.enclosingElement)) return true;
     }
     return helpersUsed.contains(element.declaration);
@@ skipping 765 matching lines @@
     return element.isNative ? jsInterceptorClass : compiler.objectClass;
   }
 
   /**
    * Unit test hook that returns code of an element as a String.
    *
    * Invariant: [element] must be a declaration element.
    */
   String assembleCode(Element element) {
     assert(invariant(element, element.isDeclaration));
+    var code = generatedCode[element];
+    if (namer is jsAst.TokenFinalizer) {
+      jsAst.TokenCounter counter = new jsAst.TokenCounter();
+      counter.countTokens(code);
+      namer.finalizeTokens();
+    }
     return jsAst.prettyPrint(generatedCode[element], compiler).getText();
   }
 
   int assembleProgram() {
     int programSize = emitter.assembleProgram();
     noSuchMethodRegistry.emitDiagnostic();
     int totalMethodCount = generatedCode.length;
     if (totalMethodCount != preMirrorsMethodCount) {
       int mirrorCount = totalMethodCount - preMirrorsMethodCount;
       double percentage = (mirrorCount / totalMethodCount) * 100;
@@ skipping 1513 matching lines @@
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 }