Enable getUserMedia to take constraints for its parameters.

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 9e74e4fa9d4b08c067295a9f561c995a7a139356..18a5a71d47d0b670fef3e6847236b753e83fd7b9 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -18834,11 +18834,22 @@ class Navigator extends NativeFieldWrapperClass1 {
    * Gets a stream (video and or audio) from the local computer.
    *
    * Use [MediaStream.supported] to check if this is supported by the current
-   * platform.
+   * platform. The arguments `audio` and `video` default to `false` (no
+   * constraints), but will accept Maps in each parameter to specify mandatory
+   * and optional constraints for the media stream. Not passing in a map, but 
+   * passing in `true` will provide a LocalMediaStream with audio or video 
+   * capabilities, but without any additional constraints.
    *
    * Example use:
    *
-   *     window.navigator.getUserMedia(audio:true, video: true).then((stream) {
+   *     window.navigator.getUserMedia(
+   *         audio: true, 
+   *         video: {'mandatory': 
+   *                    { 'minAspectRatio': 1.333, 'maxAspectRatio': 1.334 },
+   *                 'optional': 
+   *                    [{ 'minFrameRate': 60 },
+   *                     { 'maxWidth': 640 }]
+   *     }).then((stream) {
    *       var video = new VideoElement()
    *         ..autoplay = true
    *         ..src = Url.createObjectUrl(stream);
@@ -18851,8 +18862,8 @@ class Navigator extends NativeFieldWrapperClass1 {
   @DomName('Navigator.webkitGetUserMedia')
   @SupportedBrowser(SupportedBrowser.CHROME)
   @Experimental
-  Future<LocalMediaStream> getUserMedia({bool audio: false,
-      bool video: false}) {
+  Future<LocalMediaStream> getUserMedia({audio: false,
+      video: false}) {
     var completer = new Completer<LocalMediaStream>();
     var options = {
       'audio': audio,