Handle root layer fling Java-side in android_webview.

content/browser/renderer_host/render_widget_host_view_android.cc

Index: content/browser/renderer_host/render_widget_host_view_android.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_android.cc b/content/browser/renderer_host/render_widget_host_view_android.cc
index 4a8319613f9b8b58b84cbab3ee8532bdd3299ec4..4b502606857b1941fb2f321e9d45ef23465e87f0 100644
--- a/content/browser/renderer_host/render_widget_host_view_android.cc
+++ b/content/browser/renderer_host/render_widget_host_view_android.cc
@@ -875,6 +875,15 @@ void RenderWidgetHostViewAndroid::UnhandledWheelEvent(
   // intentionally empty, like RenderWidgetHostViewViews
 }
 
+void RenderWidgetHostViewAndroid::GestureEventAck(
+    int gesture_event_type,
+    InputEventAckState ack_result) {
+  if (gesture_event_type == WebKit::WebInputEvent::GestureFlingStart &&
+      ack_result == INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS) {
+    content_view_core_->UnhandledFlingStartEvent();
+  }
+}
+
 InputEventAckState RenderWidgetHostViewAndroid::FilterInputEvent(
     const WebKit::WebInputEvent& input_event) {
   if (host_) {