Support overriding fields with fields.

dart/lib/compiler/implementation/ssa/codegen.dart

Index: dart/lib/compiler/implementation/ssa/codegen.dart
diff --git a/dart/lib/compiler/implementation/ssa/codegen.dart b/dart/lib/compiler/implementation/ssa/codegen.dart
index a7ff2777c7b95b47f546c0068e4b92f052e21dcb..17cc7a9300b51d66830893d8685a58a8bb7da06a 100644
--- a/dart/lib/compiler/implementation/ssa/codegen.dart
+++ b/dart/lib/compiler/implementation/ssa/codegen.dart
@@ -190,6 +190,7 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
   SubGraph subGraph;
 
   LibraryElement get currentLibrary() => work.element.getLibrary();
+  ClassElement get currentClass() => work.element.getEnclosingClass();
   Compiler get compiler() => backend.compiler;
   NativeEmitter get nativeEmitter() => backend.emitter.nativeEmitter;
   Enqueuer get world() => backend.compiler.enqueuer.codegen;
@@ -1463,7 +1464,7 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
   visitFieldGet(HFieldGet node) {
     if (!node.isFromActivation()) {
       String name =
-          compiler.namer.instanceFieldName(currentLibrary, node.name);
+          compiler.namer.instanceFieldName(currentClass, node.name);
       beginExpression(JSPrecedence.MEMBER_PRECEDENCE);
       use(node.receiver, JSPrecedence.MEMBER_PRECEDENCE);
       buffer.add('.');
@@ -1478,7 +1479,7 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
     String name;
     if (!node.isFromActivation()) {
       name =
-          compiler.namer.instanceFieldName(currentLibrary, node.name);
+          compiler.namer.instanceFieldName(currentClass, node.name);
       beginExpression(JSPrecedence.ASSIGNMENT_PRECEDENCE);
       use(node.receiver, JSPrecedence.MEMBER_PRECEDENCE);
       buffer.add('.');