dart2js: Add --fast-startup flag.

pkg/compiler/lib/src/js_emitter/code_emitter_task.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 dart2js.js_emitter;
 
 const USE_LAZY_EMITTER = const bool.fromEnvironment("dart2js.use.lazy.emitter");
-const USE_STARTUP_EMITTER =
-    const bool.fromEnvironment("dart2js.use.startup.emitter");
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
  * The code for the containing (used) methods must exist in the `universe`.
  */
 class CodeEmitterTask extends CompilerTask {
   // TODO(floitsch): the code-emitter task should not need a namer.
   final Namer namer;
   final TypeTestRegistry typeTestRegistry;
   NativeEmitter nativeEmitter;
   MetadataCollector metadataCollector;
   Emitter emitter;
 
   /// Records if a type variable is read dynamically for type tests.
   final Set<TypeVariableElement> readTypeVariables =
       new Set<TypeVariableElement>();
 
   JavaScriptBackend get backend => compiler.backend;
 
   @deprecated
   // This field should be removed. It's currently only needed for dump-info and
   // tests.
   // The field is set after the program has been emitted.
   /// Contains a list of all classes that are emitted.
   Set<ClassElement> neededClasses;
 
-  CodeEmitterTask(Compiler compiler, Namer namer, bool generateSourceMap)
+  CodeEmitterTask(Compiler compiler, Namer namer, bool generateSourceMap,
+                  bool useStartupEmitter)
       : super(compiler),
         this.namer = namer,
         this.typeTestRegistry = new TypeTestRegistry(compiler) {
     nativeEmitter = new NativeEmitter(this);
     if (USE_LAZY_EMITTER) {
       emitter = new lazy_js_emitter.Emitter(compiler, namer, nativeEmitter);
-    } else if (USE_STARTUP_EMITTER) {
+    } else if (useStartupEmitter) {
       emitter = new startup_js_emitter.Emitter(
           compiler, namer, nativeEmitter, generateSourceMap);
     } else {
       emitter =
           new full_js_emitter.Emitter(compiler, namer, generateSourceMap, this);
     }
     metadataCollector = new MetadataCollector(compiler, emitter);
   }
 
   String get name => 'Code emitter';
@@ skipping 146 matching lines @@
   bool isConstantInlinedOrAlreadyEmitted(ConstantValue constant);
 
   /// Returns the JS code for accessing the given [constant].
   jsAst.Expression constantReference(ConstantValue constant);
 
   /// Returns the JS template for the given [builtin].
   jsAst.Template templateForBuiltin(JsBuiltin builtin);
 
   void invalidateCaches();
 }