More dart2js strong mode cleanup.

pkg/compiler/lib/src/ssa/builder_kernel.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 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart';
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry;
 import '../common/names.dart';
@@ skipping 735 matching lines @@
   // `target` for context.
   @override
   MemberElement get sourceElement => _targetStack.last;
 
   List<MemberEntity> _targetStack = <MemberEntity>[];
 
   @override
   void visitCheckLibraryIsLoaded(ir.CheckLibraryIsLoaded checkLoad) {
     HInstruction prefixConstant =
         graph.addConstantString(checkLoad.import.name, closedWorld);
-    var prefixElement = astAdapter.getElement(checkLoad.import);
+    PrefixElement prefixElement = astAdapter.getElement(checkLoad.import);
     HInstruction uriConstant = graph.addConstantString(
         prefixElement.deferredImport.uri.toString(), closedWorld);
     _pushStaticInvocation(
         _commonElements.checkDeferredIsLoaded,
         [prefixConstant, uriConstant],
         _typeInferenceMap
             .getReturnTypeOf(_commonElements.checkDeferredIsLoaded));
   }
 
   @override
@@ skipping 2704 matching lines @@
     enterBlock.setBlockFlow(
         new HTryBlockInformation(
             kernelBuilder.wrapStatementGraph(bodyGraph),
             exception,
             kernelBuilder.wrapStatementGraph(catchGraph),
             kernelBuilder.wrapStatementGraph(finallyGraph)),
         exitBlock);
     kernelBuilder.inTryStatement = previouslyInTryStatement;
   }
 }