Fix hints reported by analyzer.

pkg/compiler/lib/src/ssa/ssa_branch_builder.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 '../compiler.dart';
 import '../io/source_information.dart';
-import '../js_backend/js_backend.dart';
 import '../tree/tree.dart' as ast;
 
 import 'graph_builder.dart';
 import 'locals_handler.dart';
 import 'nodes.dart';
 
 class SsaBranch {
   final SsaBranchBuilder branchBuilder;
   final HBasicBlock block;
   LocalsHandler startLocals;
@@ skipping 202 matching lines @@
         new HSubGraphBlockInformation(elseBranch.graph));
 
     HBasicBlock conditionStartBlock = conditionBranch.block;
     conditionStartBlock.setBlockFlow(info, joinBlock);
     SubGraph conditionGraph = conditionBranch.graph;
     HIf branch = conditionGraph.end.last;
     assert(branch is HIf);
     branch.blockInformation = conditionStartBlock.blockFlow;
   }
 }