dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/native/ssa.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.
 
 import '../common.dart';
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../js/js.dart' as js;
 import '../js_backend/js_backend.dart';
-import '../js_emitter/js_emitter.dart' show CodeEmitterTask, NativeEmitter;
+import '../js_emitter/js_emitter.dart' show NativeEmitter;
 import '../ssa/builder.dart' show SsaBuilder;
 import '../ssa/nodes.dart' show HInstruction, HForeignCode, HReturn;
 import '../tree/tree.dart';
 import '../universe/side_effects.dart' show SideEffects;
 
 final RegExp nativeRedirectionRegExp = new RegExp(r'^[a-zA-Z][a-zA-Z_$0-9]*$');
 
 void handleSsaNative(SsaBuilder builder, Expression nativeBody) {
   Compiler compiler = builder.compiler;
   FunctionElement element = builder.target;
@@ skipping 95 matching lines @@
     LiteralString jsCode = nativeBody.asLiteralString();
     builder.push(new HForeignCode.statement(
         js.js.statementTemplateYielding(
             new js.LiteralStatement(jsCode.dartString.slowToString())),
         <HInstruction>[],
         new SideEffects(),
         null,
         backend.dynamicType));
   }
 }