dart2js cps: Make register allocation prioritize phi elimination.

pkg/compiler/lib/src/js_backend/codegen/task.dart

 // Copyright (c) 2014, 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.
 
 /// Generate code using the cps-based IR pipeline.
 library code_generator_task;
 
 import 'glue.dart';
 import 'codegen.dart';
 import 'unsugar.dart';
@@ skipping 261 matching lines @@
     void applyTreePass(tree_opt.Pass pass) {
       treeOptimizationTask.measureSubtask(pass.passName, () {
         pass.rewrite(node);
       });
       traceGraph(pass.passName, node);
       assert(checkTreeIntegrity(node));
     }
 
     treeOptimizationTask.measure(() {
       applyTreePass(new StatementRewriter());
-      applyTreePass(new VariableMerger());
+      applyTreePass(new VariableMerger(minifying: compiler.enableMinification));
       applyTreePass(new LoopRewriter());
       applyTreePass(new LogicalRewriter());
       applyTreePass(new PullIntoInitializers());
     });
 
     return node;
   }
 
   js.Fun compileToJavaScript(CodegenWorkItem work,
                              tree_ir.FunctionDefinition definition) {
@@ skipping 15 matching lines @@
         treeOptimizationTask]
       ..addAll(fallbackCompiler.tasks);
   }
 
   js.Node attachPosition(js.Node node, AstElement element) {
     return node.withSourceInformation(
         sourceInformationFactory.createBuilderForContext(element)
             .buildDeclaration(element));
   }
 }