Support user generated custom native JS classes.

pkg/compiler/lib/src/patch_parser.dart

Index: pkg/compiler/lib/src/patch_parser.dart
diff --git a/pkg/compiler/lib/src/patch_parser.dart b/pkg/compiler/lib/src/patch_parser.dart
index 0f3008475c1095209ef5cf8d8f547788361d14dc..fb868ba09116c26844042b84fec5c62aa5811a72 100644
--- a/pkg/compiler/lib/src/patch_parser.dart
+++ b/pkg/compiler/lib/src/patch_parser.dart
@@ -133,6 +133,8 @@ import 'elements/modelx.dart' show
     LibraryElementX,
     MetadataAnnotationX,
     SetterElementX;
+import 'js_backend/js_backend.dart' show
+    JavaScriptBackend;
 import 'library_loader.dart' show
     LibraryLoader;
 import 'parser/listener.dart' show
@@ -304,6 +306,7 @@ void patchElement(Compiler compiler,
         patch, MessageKind.PATCH_NON_EXISTING, {'name': patch.name});
     return;
   }
+
   if (!(origin.isClass ||
         origin.isConstructor ||
         origin.isFunction ||
@@ -359,6 +362,12 @@ checkNativeAnnotation(Compiler compiler, ClassElement cls) {
       const NativeAnnotationHandler());
 }
 
+checkJsInteropAnnotation(Compiler compiler, element) {
+  EagerAnnotationHandler.checkAnnotation(compiler, element,
+      const JsInteropAnnotationHandler());
+}
+
+
 /// Abstract interface for pre-resolution detection of metadata.
 ///
 /// The detection is handled in two steps:
@@ -394,12 +403,19 @@ abstract class EagerAnnotationHandler<T> {
       if (result != null) {
         // TODO(johnniwinther): Perform this check in
         // [Compiler.onLibrariesLoaded].
-        compiler.enqueuer.resolution.addDeferredAction(element, () {
+        // TODO(jacobr): annotation resolution needs to be refactored.
+        actionCallback() {
           annotation.ensureResolved(compiler);
           handler.validate(
               compiler, element, annotation,
               compiler.constants.getConstantValue(annotation.constant));
-        });
+        }
+        if (compiler.enqueuer.resolution.queueIsClosed) {
+          actionCallback();
+        } else {
+          compiler.enqueuer.resolution.addDeferredAction(element,
+              actionCallback);
+        }
         return result;
       }
     }
@@ -449,6 +465,57 @@ class NativeAnnotationHandler implements EagerAnnotationHandler<String> {
   }
 }
 
+/// Annotation handler for pre-resolution detection of `@Js(...)`
+/// annotations.
+class JsInteropAnnotationHandler implements EagerAnnotationHandler<String> {
+  const JsInteropAnnotationHandler();
+
+  // TODO(jacobr): this method is pure technical debt.
+  String dietResolveStringToken(StringToken token) {
+    String value = token.value;
+    if ((value.startsWith('"') && value.endsWith('"')) ||
+        value.startsWith("'") && value.endsWith("'")) {
+      return value.substring(1, value.length - 1);
+    } else {
+      throw 'Invalid @Js(...) annotation. Unexpected name: $value';
+    }
+  }
+
+  String getJsNameAnnotation(MetadataAnnotation annotation) {
+    if (annotation.beginToken != null &&
+        annotation.beginToken.next.value == 'Js') {
+      // Skipping '@', 'Js', and '('.
+      Token argument = annotation.beginToken.next.next.next;
+      return (argument is StringToken) ? dietResolveStringToken(argument) : '';
+    }
+
+    return null;
+  }
+
+  String apply(Compiler compiler,
+             Element element,
+             MetadataAnnotation annotation) {
+    String jsName = getJsNameAnnotation(annotation);
+    if (jsName != null) {
+      element.setJsInterop(jsName);
+      element.declaration.setJsInterop(jsName);
+    }
+    return jsName;
+  }
+
+  @override
+  void validate(Compiler compiler,
+                Element element,
+                MetadataAnnotation annotation,
+                ConstantValue constant) {
+    JavaScriptBackend backend = compiler.backend;
+    if (constant.getType(compiler.coreTypes).element !=
+        backend.jsAnnotationClass) {
+      compiler.internalError(annotation, 'Invalid @Js(...) annotation.');
+    }
+  }
+}
+
 /// Annotation handler for pre-resolution detection of `@patch` annotations.
 class PatchAnnotationHandler implements EagerAnnotationHandler<PatchVersion> {
   const PatchAnnotationHandler();