Add @Native(...) annotation for native class names.

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

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compiler.dart b/sdk/lib/_internal/compiler/implementation/compiler.dart
index f01e964e510c102b25e6a3608f369ab65fb95766..97393bc1631083f89555bf3888acc5d048c7e99d 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -389,6 +389,13 @@ abstract class Backend {
         return compiler.patchParser.patchLibrary(loader, patchUri, library);
       }
     }
+    if (library.canUseNative) {
+      library.forEachLocalMember((Element element) {
+        if (element.isClass) {
+          checkNativeAnnotation(compiler, element);
+        }
+      });
+    }
     return new Future.value();
   }
 
@@ -722,6 +729,9 @@ abstract class Compiler implements DiagnosticListener {
   /// The constant for the [patch] variable defined in dart:_js_helper.
   Constant patchConstant;
 
+  // TODO(johnniwinther): Move this to the JavaScriptBackend.
+  ClassElement nativeAnnotationClass;
+
   // Initialized after symbolClass has been resolved.
   FunctionElement symbolConstructor;
 
@@ -1118,6 +1128,8 @@ abstract class Compiler implements DiagnosticListener {
       deferredLibraryClass = findRequiredElement(library, 'DeferredLibrary');
     } else if (uri == DART_NATIVE_TYPED_DATA) {
       typedDataClass = findRequiredElement(library, 'NativeTypedData');
+    } else if (uri == js_backend.JavaScriptBackend.DART_JS_HELPER) {
+      nativeAnnotationClass = findRequiredElement(library, 'Native');
     }
     return backend.onLibraryScanned(library, loader);
   }