Implement CancelUserMediaRequest for the browser part

content/browser/renderer_host/media/media_stream_dispatcher_host.cc

Index: content/browser/renderer_host/media/media_stream_dispatcher_host.cc
diff --git a/content/browser/renderer_host/media/media_stream_dispatcher_host.cc b/content/browser/renderer_host/media/media_stream_dispatcher_host.cc
index 96eeb256c9fd05be6cf1c7d0b387b227f6ac4c8f..fd980c524dedf5283dea9edc7813c96339fe6ba4 100644
--- a/content/browser/renderer_host/media/media_stream_dispatcher_host.cc
+++ b/content/browser/renderer_host/media/media_stream_dispatcher_host.cc
@@ -214,8 +214,13 @@ void MediaStreamDispatcherHost::OnCancelGenerateStream(int render_view_id,
   DVLOG(1) << "MediaStreamDispatcherHost::OnCancelGenerateStream("
            << render_view_id << ", "
            << page_request_id << ")";
-  // TODO(perkj): Implement
-  NOTIMPLEMENTED();
+
+  for (StreamMap::iterator it = streams_.begin(); it != streams_.end(); ++it) {
+    if (it->second.render_view_id == render_view_id &&
+        it->second.page_request_id == page_request_id) {
+      manager()->CancelGenerateStream(it->first);
+    }
+  }
 }
 
 void MediaStreamDispatcherHost::OnStopGeneratedStream(