Remove a few warnings.

lib/compiler/implementation/ssa/codegen.dart

 // Copyright (c) 2012, 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.
 
 class SsaCodeGeneratorTask extends CompilerTask {
   final JavaScriptBackend backend;
   SsaCodeGeneratorTask(JavaScriptBackend backend)
       : this.backend = backend,
         super(backend.compiler);
   String get name() => 'SSA code generator';
   NativeEmitter get nativeEmitter() => backend.emitter.nativeEmitter;
 
 
   js.Fun buildJavaScriptFunction(FunctionElement element,
                                  List<js.Parameter> parameters,
                                  js.Block body) {
     FunctionExpression expression = element.cachedNode;
     js.Fun result = new js.Fun(parameters, body);
     result.sourcePosition = expression.getBeginToken();
     result.endSourcePosition = expression.getEndToken();
     return result;
   }
 
   CodeBuffer prettyPrint(js.Node node, Element positionElement) {
     return js.prettyPrint(node, compiler, positionElement);
   }
 
   CodeBuffer generateMethod(WorkItem work, HGraph graph) {
     return measure(() {
-      HTypeMap types = work.compilationContext.types;
+      JavaScriptItemCompilationContext context = work.compilationContext;
+      HTypeMap types = context.types;
       graph.exit.predecessors.forEach((block) {
         assert(block.last is HGoto || block.last is HReturn);
         if (block.last is HReturn) {
           backend.registerReturnType(work.element, types[block.last.inputs[0]]);
         } else {
           backend.registerReturnType(work.element, HType.NULL);
         }
       });
       compiler.tracer.traceGraph("codegen", graph);
       Map<Element, String> parameterNames = getParameterNames(work);
@@ skipping 2865 matching lines @@
   if (leftType.canBeNull() && rightType.canBeNull()) {
     if (left.isConstantNull() || right.isConstantNull() ||
         (leftType.isPrimitive() && leftType == rightType)) {
       return '==';
     }
     return null;
   } else {
     return '===';
   }
 }