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 b3778465137137e10f9fc1613555cea6f6bc4da3..f1dde53d7f0f36950030d67d6dd4abf95f95b3b9 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
@@ -1722,7 +1722,7 @@ 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 = _fieldPropertyName(node.element);
       push(new js.PropertyAccess.field(pop(), name), node);
       HType receiverHType = types[node.receiver];
       DartType type = receiverHType.computeType(compiler);
@@ -1734,7 +1734,7 @@ abstract class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
   }
 
   visitFieldSet(HFieldSet node) {
-    String name = backend.namer.getName(node.element);
+    String name = _fieldPropertyName(node.element);
     DartType type = types[node.receiver].computeType(compiler);
     if (type != null) {
       // Field setters in the generative constructor body are handled in a
@@ -1750,9 +1750,13 @@ abstract class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
     js.Expression receiver = pop();
     use(node.value);
     push(new js.Assignment(new js.PropertyAccess.field(receiver, name), pop()),
-         node);
+        node);
   }
 
+  String _fieldPropertyName(Element element) => element.isNative()
+      ? element.nativeName()
+      : backend.namer.getName(element);
+
   visitLocalGet(HLocalGet node) {
     use(node.receiver);
   }