Filter GestureFlingStarts with Vx=Vy=0 in RenderWidgetHostViewChildFrame

content/browser/frame_host/render_widget_host_view_child_frame.cc

Index: content/browser/frame_host/render_widget_host_view_child_frame.cc
diff --git a/content/browser/frame_host/render_widget_host_view_child_frame.cc b/content/browser/frame_host/render_widget_host_view_child_frame.cc
index 09f1353e453a7a173507f4aff28078083853de7d..7e7f8e6eea58ad06e0aa1f3c9d93c25806ff3340 100644
--- a/content/browser/frame_host/render_widget_host_view_child_frame.cc
+++ b/content/browser/frame_host/render_widget_host_view_child_frame.cc
@@ -33,6 +33,7 @@
 #include "content/public/browser/render_process_host.h"
 #include "content/public/common/browser_plugin_guest_mode.h"
 #include "gpu/ipc/common/gpu_messages.h"
+#include "third_party/WebKit/public/web/WebInputEvent.h"
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/geometry/size_f.h"
 
@@ -655,6 +656,28 @@ void RenderWidgetHostViewChildFrame::OnSetNeedsBeginFrames(
   }
 }
 
+InputEventAckState RenderWidgetHostViewChildFrame::FilterInputEvent(
+    const blink::WebInputEvent& input_event) {
+  if (input_event.type == blink::WebInputEvent::GestureFlingStart) {
+    const blink::WebGestureEvent& gesture_event =
+        static_cast<const blink::WebGestureEvent&>(input_event);
+    // Zero-velocity touchpad flings are an Aura-specific signal that the
+    // touchpad scroll has ended, and should not be forwarded to the renderer.
+    if (gesture_event.sourceDevice == blink::WebGestureDeviceTouchpad &&
+        !gesture_event.data.flingStart.velocityX &&
+        !gesture_event.data.flingStart.velocityY) {
+      // Reporting consumed for a fling suggests that there's now an *active*

[Charlie Reis, 2016/07/22 17:25:55]

nit: Can you rephrase?  I'm not sure what "Reporting consumed for a fling
suggests" means.

+      // fling that requires both animation and a fling-end notification.
+      // However, here we've just indicated touchpad scroll has ended, and
+      // we're not going to actually tick a fling animation. Report no consumer

[Charlie Reis, 2016/07/22 17:25:55]

tick?

+      // to convey this.
+      return INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS;
+    }
+  }
+
+  return INPUT_EVENT_ACK_STATE_NOT_CONSUMED;
+}
+
 BrowserAccessibilityManager*
 RenderWidgetHostViewChildFrame::CreateBrowserAccessibilityManager(
     BrowserAccessibilityDelegate* delegate, bool for_root_frame) {