Add @JSName annotation for native fields and methods.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart b/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
index d51850f9278c5bdf8c0d734084f33b01ffe699b8..69805d3d70ff79e7fe9bb9aaf4fa13706e0d38da 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
@@ -1729,7 +1729,9 @@ abstract class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
       // property should not be mangled.
       push(new js.PropertyAccess.field(pop(), 'length'), node);
     } else {
-      String name = backend.namer.getName(node.element);
+      String name = node.element.isNative()
+          ? node.element.nativeName()
+          : backend.namer.getName(node.element);
       push(new js.PropertyAccess.field(pop(), name), node);
       HType receiverHType = types[node.receiver];
       DartType type = receiverHType.computeType(compiler);
@@ -1741,7 +1743,9 @@ abstract class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
   }
 
   visitFieldSet(HFieldSet node) {
-    String name = backend.namer.getName(node.element);
+    String name = node.element.isNative()
+        ? node.element.nativeName()
+        : backend.namer.getName(node.element);
     DartType type = types[node.receiver].computeType(compiler);
     if (type != null) {
       // Field setters in the generative constructor body are handled in a