Do not coalesce events received before and after a kRelativeMotionEvent

When a WebCoalescedInputEvent is getting built from individual input
events by the renderer, it looks for events that can be coalesced together.
If there is a kRelativeMotionEvent in the queue, existing logic is to
skip it and coalesce the next events. In case of a pointer lock,
kRelativeMotionEvent is sent during a cursor recenter. Events before
kRelativeMotionEvent and events after kRelativeMotionEvent differ by a big
margin and should not be coalesced together.

This patch correctly stops coalescing when a kRelativeMotionEvent is seen
thereby avoiding incorrect bigdeltas from being sent to the DOM.

Bug: 1066544
Change-Id: I1a38391e41f4d0bc11ec67c88e3df1d321bc15bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2226479Reviewed-by: Ella Ge <eirage@chromium.org>
Reviewed-by: Mustaq Ahmed <mustaq@chromium.org>
Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Reviewed-by: Vincent Scheib <scheib@chromium.org>
Commit-Queue: Mustaq Ahmed <mustaq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774654}

content/renderer/input/main_thread_event_queue.cc

@@ -63,15 +63,24 @@ class QueuedWebInputEvent : public MainThreadEventQueueTask {
 
   ~QueuedWebInputEvent() override {}
 
-  bool ArePointerMoveEventTypes(QueuedWebInputEvent* other_event) {
+  bool AreCoalescablePointerRawUpdateEvents(QueuedWebInputEvent* other_event) {
     // There is no pointermove at this point in the queue.
     DCHECK(event_->Event().GetType() != WebInputEvent::Type::kPointerMove &&
            other_event->event_->Event().GetType() !=
                WebInputEvent::Type::kPointerMove);
+    // Events with modifiers differing by kRelativeMotionEvent should not be
+    // coalesced. In case of a pointer lock, kRelativeMotionEvent is sent
+    // when the cursor is recentered. Events post the recentered event have
+    // a big delta compared to the previous events and hence should not be
+    // coalesced.
     return event_->Event().GetType() ==
                WebInputEvent::Type::kPointerRawUpdate &&
            other_event->event_->Event().GetType() ==
-               WebInputEvent::Type::kPointerRawUpdate;
+               WebInputEvent::Type::kPointerRawUpdate &&
+           ((event_->Event().GetModifiers() &
+             blink::WebInputEvent::Modifiers::kRelativeMotionEvent) ==
+            (other_event->event_->Event().GetModifiers() &
+             blink::WebInputEvent::Modifiers::kRelativeMotionEvent));
   }
 
   FilterResult FilterNewEvent(MainThreadEventQueueTask* other_task) override {
@@ -92,7 +101,7 @@ class QueuedWebInputEvent : public MainThreadEventQueueTask {
       // Two pointerevents may not be able to coalesce but we should continue
       // looking further down the queue if both of them were rawupdate or move
       // events and only their pointer_type, id, or event_type was different.
-      if (ArePointerMoveEventTypes(other_event))
+      if (AreCoalescablePointerRawUpdateEvents(other_event))
         return FilterResult::KeepIterating;
       return FilterResult::StopIterating;
     }