dart2js: Add --fast-startup flag.

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 604 matching lines @@
 
   JavaScriptResolutionCallbacks resolutionCallbacks;
 
   PatchResolverTask patchResolverTask;
 
   bool enabledNoSuchMethod = false;
 
   final SourceInformationStrategy sourceInformationStrategy;
 
   JavaScriptBackend(Compiler compiler,
-                    {bool generateSourceMap: true})
+                    {bool generateSourceMap: true,
+                     bool useStartupEmitter: false})
       : namer = determineNamer(compiler),
         oneShotInterceptors = new Map<jsAst.Name, Selector>(),
         interceptedElements = new Map<String, Set<Element>>(),
         rti = new RuntimeTypes(compiler),
         specializedGetInterceptors = new Map<jsAst.Name, Set<ClassElement>>(),
         annotations = new Annotations(compiler),
         this.sourceInformationStrategy =
             generateSourceMap
                 ? (useNewSourceInfo
                      ? const PositionSourceInformationStrategy()
                      : const StartEndSourceInformationStrategy())
                 : const JavaScriptSourceInformationStrategy(),
         super(compiler) {
-    emitter = new CodeEmitterTask(compiler, namer, generateSourceMap);
+    emitter = new CodeEmitterTask(
+        compiler, namer, generateSourceMap, useStartupEmitter);
     typeVariableHandler = new TypeVariableHandler(compiler);
     customElementsAnalysis = new CustomElementsAnalysis(this);
     noSuchMethodRegistry = new NoSuchMethodRegistry(this);
     constantCompilerTask = new JavaScriptConstantTask(compiler);
     resolutionCallbacks = new JavaScriptResolutionCallbacks(this);
     patchResolverTask = new PatchResolverTask(compiler);
     functionCompiler = compiler.useCpsIr
          ? new CpsFunctionCompiler(
              compiler, this, sourceInformationStrategy)
          : new SsaFunctionCompiler(this, sourceInformationStrategy);
@@ skipping 2361 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);
 }