Fix hints reported by analyzer.

pkg/compiler/lib/src/ssa/locals_handler.dart

 // Copyright (c) 2016, 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 '../closure.dart';
 import '../common.dart';
 import '../compiler.dart' show Compiler;
 import '../elements/resolution_types.dart';
 import '../elements/elements.dart';
 import '../io/source_information.dart';
@@ skipping 464 matching lines @@
     }
   }
 
   /// Create phis at the loop entry for local variables (ready for the values
   /// from the back edge).  Populate the phis with the current values.
   void beginLoopHeader(HBasicBlock loopEntry) {
     // Create a copy because we modify the map while iterating over it.
     Map<Local, HInstruction> savedDirectLocals =
         new Map<Local, HInstruction>.from(directLocals);
 
-    JavaScriptBackend backend = _compiler.backend;
     // Create phis for all elements in the definitions environment.
     savedDirectLocals.forEach((Local local, HInstruction instruction) {
       if (isAccessedDirectly(local)) {
         // We know 'this' cannot be modified.
         if (local != closureData.thisLocal) {
           HPhi phi =
               new HPhi.singleInput(local, instruction, commonMasks.dynamicType);
           loopEntry.addPhi(phi);
           directLocals[local] = phi;
         } else {
@@ skipping 166 matching lines @@
   final ExecutableElement executableContext;
 
   // Avoid slow Object.hashCode.
   final int hashCode = _nextHashCode = (_nextHashCode + 1).toUnsigned(30);
   static int _nextHashCode = 0;
 
   SyntheticLocal(this.name, this.executableContext);
 
   toString() => 'SyntheticLocal($name)';
 }