Move middle-click autoscroll to synthetic fling.

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index 6fc9ba071362fce5c174ce9b9b7ee4721a4decac..4ada1b4d8be6773638ca7b15cd20abd940bb59b6 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -682,7 +682,8 @@ WebInputEventResult WebViewImpl::HandleGestureEvent(
               ->GetEventHandler()
               .IsScrollbarHandlingGestures())
         break;
-      EndActiveFlingAnimation();
+      if (event.source_device != kWebGestureDeviceSyntheticAutoscroll)
+        EndActiveFlingAnimation();
       position_on_fling_start_ = WebPoint(event.x, event.y);
       global_position_on_fling_start_ =
           WebPoint(event.global_x, event.global_y);
@@ -1983,10 +1984,12 @@ void WebViewImpl::BeginFrame(double last_frame_time_monotonic) {
       WebGestureDevice last_fling_source_device = fling_source_device_;
       EndActiveFlingAnimation();
 
-      WebGestureEvent end_scroll_event = CreateGestureScrollEventFromFling(
-          WebInputEvent::kGestureScrollEnd, last_fling_source_device);
-      MainFrameImpl()->GetFrame()->GetEventHandler().HandleGestureScrollEnd(
-          end_scroll_event);
+      if (last_fling_source_device != kWebGestureDeviceSyntheticAutoscroll) {
+        WebGestureEvent end_scroll_event = CreateGestureScrollEventFromFling(
+            WebInputEvent::kGestureScrollEnd, last_fling_source_device);
+        MainFrameImpl()->GetFrame()->GetEventHandler().HandleGestureScrollEnd(
+            end_scroll_event);
+      }
     }
   }