Fixing a number of Dart2JS compiler warnings.

sdk/lib/html/html_common/conversions.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 // Conversions for IDBKey.
 //
 // Per http://www.w3.org/TR/IndexedDB/#key-construct
 //
 // "A value is said to be a valid key if it is one of the following types: Array
@@ skipping 296 matching lines @@
 
     // Assume anything else is already a valid Dart object, either by having
     // already been processed, or e.g. a clonable native class.
     return e;
   }
 
   var copy = walk(object);
   return copy;
 }
 
+// Conversions for ImageData
+//
+// On Firefox, the returned ImageData is a plain object.
+
+class _TypedImageData implements ImageData {
+  final Uint8ClampedList data;
+  final int height;
+  final int width;
+
+  _TypedImageData(this.data, this.height, this.width);
+}
+
+ImageData convertNativeToDart_ImageData(nativeImageData) {
+
+  // None of the native getters that return ImageData have the type ImageData
+  // since that is incorrect for FireFox (which returns a plain Object).  So we
+  // need something that tells the compiler that the ImageData class has been
+  // instantiated.
+  // TODO(sra): Remove this when all the ImageData returning APIs have been
+  // annotated as returning the union ImageData + Object.
+  JS('ImageData', '0');
+
+  if (nativeImageData is ImageData) return nativeImageData;
+
+  // On Firefox the above test fails because imagedata is a plain object.
+  // So we create a _TypedImageData.
+
+  return new _TypedImageData(
+      JS('var', '#.data', nativeImageData),
+      JS('var', '#.height', nativeImageData),
+      JS('var', '#.width', nativeImageData));
+}
+
+// We can get rid of this conversion if _TypedImageData implements the fields
+// with native names.
+convertDartToNative_ImageData(ImageData imageData) {
+  if (imageData is _TypedImageData) {
+    return JS('', '{data: #, height: #, width: #}',
+        imageData.data, imageData.height, imageData.width);
+  }
+  return imageData;
+}
+
 
 bool isJavaScriptDate(value) => JS('bool', '# instanceof Date', value);
 bool isJavaScriptRegExp(value) => JS('bool', '# instanceof RegExp', value);
 bool isJavaScriptArray(value) => JS('bool', '# instanceof Array', value);
 bool isJavaScriptSimpleObject(value) =>
     JS('bool', 'Object.getPrototypeOf(#) === Object.prototype', value);
 bool isImmutableJavaScriptArray(value) =>
     JS('bool', r'!!(#.immutable$list)', value);
 
 
 
 const String _serializedScriptValue =
     'num|String|bool|'
     '=List|=Object|'
     'Blob|File|ByteBuffer|TypedData'
     // TODO(sra): Add Date, RegExp.
     ;
 const annotation_Creates_SerializedScriptValue =
     const Creates(_serializedScriptValue);
 const annotation_Returns_SerializedScriptValue =
     const Returns(_serializedScriptValue);