Ignored inertial scroll (fling) event should ignore in ReceivedEventACK()

An inertial scroll (fling) event from previous completed overscroll
gesture sequence should not modify scroll state in ReceivedEventACK().

Bug: 647140
Change-Id: I48c595124c7f0e2e37b92d256ab13dc50a1ec400
Reviewed-on: https://chromium-review.googlesource.com/1003214
Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Mohsen Izadi <mohsen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549586}

content/browser/renderer_host/overscroll_controller.cc

@@ -84,6 +84,19 @@ bool OverscrollController::ShouldProcessEvent(
   return true;
 }
 
+bool OverscrollController::ShouldIgnoreInertialEvent(
+    const blink::WebInputEvent& event) const {
+  if (!ignore_following_inertial_events_ ||
+      event.GetType() != blink::WebInputEvent::kGestureScrollUpdate) {
+    return false;
+  }
+
+  const blink::WebGestureEvent& gesture =
+      static_cast<const blink::WebGestureEvent&>(event);
+  return gesture.data.scroll_update.inertial_phase ==
+         blink::WebGestureEvent::kMomentumPhase;
+}
+
 bool OverscrollController::WillHandleEvent(const blink::WebInputEvent& event) {
   if (event.GetType() == blink::WebInputEvent::kGestureScrollBegin)
     ignore_following_inertial_events_ = false;
@@ -104,15 +117,8 @@ bool OverscrollController::WillHandleEvent(const blink::WebInputEvent& event) {
 
   // Consume the scroll-update events if they are from a inertial scroll (fling)
   // event that completed an overscroll gesture.
-  if (ignore_following_inertial_events_ &&
-      event.GetType() == blink::WebInputEvent::kGestureScrollUpdate) {
-    const blink::WebGestureEvent& gesture =
-        static_cast<const blink::WebGestureEvent&>(event);
-    if (gesture.data.scroll_update.inertial_phase ==
-        blink::WebGestureEvent::kMomentumPhase) {
-      return true;
-    }
-  }
+  if (ShouldIgnoreInertialEvent(event))
+    return true;
 
   bool reset_scroll_state = false;
   if (scroll_state_ != ScrollState::NONE || overscroll_delta_x_ ||
@@ -175,6 +181,11 @@ void OverscrollController::ReceivedEventACK(const blink::WebInputEvent& event,
   if (!ShouldProcessEvent(event))
     return;
 
+  // An inertial scroll (fling) event from a completed overscroll gesture
+  // should not modify states below.
+  if (ShouldIgnoreInertialEvent(event))
+    return;
+
   if (processed) {
     // If a scroll event is consumed by the page, i.e. some content on the page
     // has been scrolled, then there is not going to be an overscroll gesture,

content/browser/renderer_host/overscroll_controller.h

@@ -122,6 +122,9 @@ class CONTENT_EXPORT OverscrollController {
   // triggered the overscroll gesture.
   void SetOverscrollMode(OverscrollMode new_mode, OverscrollSource source);
 
+  // Whether this inertial event should be filtered out by the controller.
+  bool ShouldIgnoreInertialEvent(const blink::WebInputEvent& event) const;
+
   // Whether this event should be processed or not handled by the controller.
   bool ShouldProcessEvent(const blink::WebInputEvent& event);
 

content/browser/renderer_host/overscroll_controller_unittest.cc

@@ -157,9 +157,9 @@ TEST_F(OverscrollControllerTest,
   EXPECT_FALSE(SimulateGestureScrollUpdate(
       100, 0, blink::kWebGestureDeviceTouchpad, true));
   SimulateAck(false);
-  EXPECT_EQ(OVERSCROLL_EAST, controller_mode());
-  EXPECT_EQ(OverscrollSource::TOUCHPAD, controller_source());
-  EXPECT_EQ(OVERSCROLL_EAST, delegate()->current_mode());
+  EXPECT_EQ(OVERSCROLL_NONE, controller_mode());
+  EXPECT_EQ(OverscrollSource::NONE, controller_source());
+  EXPECT_EQ(OVERSCROLL_NONE, delegate()->current_mode());
   EXPECT_EQ(OVERSCROLL_EAST, delegate()->completed_mode());
 
   // Next Inertial update event would be consumed by overscroll controller.