Implement Wheel Gesture Scrolling on OSX.

content/browser/renderer_host/input/mouse_wheel_event_queue.cc

Index: content/browser/renderer_host/input/mouse_wheel_event_queue.cc
diff --git a/content/browser/renderer_host/input/mouse_wheel_event_queue.cc b/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
index 48dbad231bb553d57a13efc79263eecab3a69f64..8e77365d5d2859e5c6f0e1bcdee40bd3fc884257 100644
--- a/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
+++ b/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
@@ -85,6 +85,9 @@ void MouseWheelEventQueue::ProcessMouseWheelAck(
       (scrolling_device_ == blink::WebGestureDeviceUninitialized ||
        scrolling_device_ == blink::WebGestureDeviceTouchpad)) {
     GestureEventWithLatencyInfo scroll_update;
+    scroll_update.event.timeStampSeconds =
+        (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();

[tdresser, 2016/03/02 18:26:53]

We should take the timestamp from the wheel event. (We use the touch event
timestamps for gesture events).

[dtapuska, 2016/03/07 18:03:59]

Done.

+
     scroll_update.event.x = event_sent_for_gesture_ack_->event.x;
     scroll_update.event.y = event_sent_for_gesture_ack_->event.y;
     scroll_update.event.globalX = event_sent_for_gesture_ack_->event.globalX;
@@ -96,6 +99,9 @@ void MouseWheelEventQueue::ProcessMouseWheelAck(
         event_sent_for_gesture_ack_->event.deltaX;
     scroll_update.event.data.scrollUpdate.deltaY =
         event_sent_for_gesture_ack_->event.deltaY;
+    scroll_update.event.data.scrollUpdate.inertial =
+        event_sent_for_gesture_ack_->event.momentumPhase !=
+        blink::WebMouseWheelEvent::PhaseNone;

[tdresser, 2016/03/02 18:26:53]

What's the momentum phase for non-mac?
Maybe add a comment?

[dtapuska, 2016/03/07 18:03:59]

Done.

     if (event_sent_for_gesture_ack_->event.scrollByPage) {
       scroll_update.event.data.scrollUpdate.deltaUnits =
           blink::WebGestureEvent::Page;
@@ -114,7 +120,30 @@ void MouseWheelEventQueue::ProcessMouseWheelAck(
               ? blink::WebGestureEvent::PrecisePixels
               : blink::WebGestureEvent::Pixels;
     }
-    SendGesture(scroll_update);
+
+    bool send_end_now = false;
+    bool schedule_end = true;
+
+    if (event_sent_for_gesture_ack_->event.phase !=
+            blink::WebMouseWheelEvent::PhaseNone ||
+        event_sent_for_gesture_ack_->event.momentumPhase !=
+            blink::WebMouseWheelEvent::PhaseNone) {
+      schedule_end = false;
+      send_end_now = event_sent_for_gesture_ack_->event.phase ==
+                         blink::WebMouseWheelEvent::PhaseEnded ||
+                     event_sent_for_gesture_ack_->event.phase ==
+                         blink::WebMouseWheelEvent::PhaseCancelled ||
+                     event_sent_for_gesture_ack_->event.momentumPhase ==
+                         blink::WebMouseWheelEvent::PhaseEnded ||
+                     event_sent_for_gesture_ack_->event.momentumPhase ==
+                         blink::WebMouseWheelEvent::PhaseCancelled;
+    }
+
+    if (scroll_update.event.data.scrollUpdate.deltaX != 0 ||
+        scroll_update.event.data.scrollUpdate.deltaY != 0)
+      SendGesture(scroll_update, schedule_end);
+    if (send_end_now)
+      SendScrollEnd(scroll_update.event);
   }
 
   event_sent_for_gesture_ack_.reset();
@@ -160,6 +189,8 @@ void MouseWheelEventQueue::TryForwardNextEventToRenderer() {
 
 void MouseWheelEventQueue::SendScrollEnd(blink::WebGestureEvent update_event) {
   GestureEventWithLatencyInfo scroll_end;
+  scroll_end.event.timeStampSeconds =
+      (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();

[tdresser, 2016/03/02 18:26:53]

I suppose this timestamp needs to be made up, unfortunately.

[dtapuska, 2016/03/07 18:03:59]

Acknowledged.

   scroll_end.event.type = WebInputEvent::GestureScrollEnd;
   scroll_end.event.sourceDevice = blink::WebGestureDeviceTouchpad;
   scroll_end.event.resendingPluginId = -1;
@@ -170,20 +201,24 @@ void MouseWheelEventQueue::SendScrollEnd(blink::WebGestureEvent update_event) {
   scroll_end.event.globalX = update_event.globalX;
   scroll_end.event.globalY = update_event.globalY;
 
-  SendGesture(scroll_end);
+  SendGesture(scroll_end, false);
 }
 
 void MouseWheelEventQueue::SendGesture(
-    const GestureEventWithLatencyInfo& gesture) {
+    const GestureEventWithLatencyInfo& gesture,
+    bool generate_end) {
   switch (gesture.event.type) {
     case WebInputEvent::GestureScrollUpdate:
       if (needs_scroll_begin_) {
         GestureEventWithLatencyInfo scroll_begin(gesture);
+        scroll_begin.event.timeStampSeconds = gesture.event.timeStampSeconds;
         scroll_begin.event.x = gesture.event.x;
         scroll_begin.event.y = gesture.event.y;
         scroll_begin.event.globalX = gesture.event.globalX;
         scroll_begin.event.globalY = gesture.event.globalY;
         scroll_begin.event.type = WebInputEvent::GestureScrollBegin;
+        scroll_begin.event.data.scrollBegin.inertial =
+            gesture.event.data.scrollUpdate.inertial;

[tdresser, 2016/03/02 18:26:53]

It isn't clear to me when we'd need a scroll begin but have an inertial update.

When will this happen?

[dtapuska, 2016/03/07 18:03:59]

So the way phasing is done on OSX is that the phase terminates and it doesn't
transition into the inertial state via a GSU... ie; it will be:
GSB (inertial = false)
GSU (inertial = false)
GSE 
GSB (inertial = true)
GSU (inertial = true)
GSE

If we wanted to avoid the GSE/GSB in the middle we could hold onto generating
the GSE not based on when the phases change but based on a timer. However I have
seen events not generate a momentum phase and just terminate. So in those cases
the GSE would be delayed by the timer. This seemed to be the best compromise;
and it was similar to the events requested in here:
https://github.com/w3c/uievents/issues/58

         scroll_begin.event.data.scrollBegin.deltaXHint =
             gesture.event.data.scrollUpdate.deltaX;
         scroll_begin.event.data.scrollBegin.deltaYHint =
@@ -192,11 +227,12 @@ void MouseWheelEventQueue::SendGesture(
         scroll_begin.event.data.scrollBegin.deltaHintUnits =
             gesture.event.data.scrollUpdate.deltaUnits;
 
-        SendGesture(scroll_begin);
+        SendGesture(scroll_begin, false);
       }
-      if (scroll_end_timer_.IsRunning()) {
+      if (scroll_end_timer_.IsRunning())
         scroll_end_timer_.Reset();
-      } else {
+
+      if (generate_end) {
         scroll_end_timer_.Start(
             FROM_HERE,
             base::TimeDelta::FromMilliseconds(scroll_transaction_ms_),