x11: Bring back MontionNotify events coalescing

MontionNotify XEvents coalescing logic has been accidentally lost after
the PlatformEvent migration CLs have landed (crbug.com/965991), what
leads to some performance hit/regressions. This patch adds it back as an
attempt to address regressions reported at crbug.com/1051325. Even
though the numbers the report seem quite noisy and unstable, [1] shows
that this was the major cause for such perf regression.

R=thomasanderson@chromium.org

[1] https://pinpoint-dot-chromeperf.appspot.com/job/172c2f5a620000

Bug: 1051325, 965991
Change-Id: Ib5d06867d97633c3593584222571b8d910deb304
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062098Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Nick Yamane <nickdiego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#742892}

ui/base/x/x11_util.cc

@@ -358,15 +358,34 @@ XcursorImage* SkBitmapToXcursorImage(const SkBitmap* cursor_image,
 }
 
 int CoalescePendingMotionEvents(const XEvent* xev, XEvent* last_event) {
-  XIDeviceEvent* xievent = static_cast<XIDeviceEvent*>(xev->xcookie.data);
-  int num_coalesced = 0;
+  DCHECK(xev->type == MotionNotify || xev->type == GenericEvent);
   XDisplay* display = xev->xany.display;
-  int event_type = xev->xgeneric.evtype;
+  XEvent next_event;
+  bool is_motion = false;
+  int num_coalesced = 0;
 
+  if (xev->type == MotionNotify) {
+    is_motion = true;
+    while (XPending(display)) {
+      XPeekEvent(xev->xany.display, &next_event);
+      // Discard all but the most recent motion event that targets the same
+      // window with unchanged state.
+      if (next_event.type == MotionNotify &&
+          next_event.xmotion.window == xev->xmotion.window &&
+          next_event.xmotion.subwindow == xev->xmotion.subwindow &&
+          next_event.xmotion.state == xev->xmotion.state) {
+        XNextEvent(xev->xany.display, last_event);
+      } else {
+        break;
+      }
+    }
+  } else {
+    int event_type = xev->xgeneric.evtype;
+    XIDeviceEvent* xievent = static_cast<XIDeviceEvent*>(xev->xcookie.data);
     DCHECK(event_type == XI_Motion || event_type == XI_TouchUpdate);
+    is_motion = event_type == XI_Motion;
 
     while (XPending(display)) {
-    XEvent next_event;
       XPeekEvent(display, &next_event);
 
       // If we can't get the cookie, abort the check.
@@ -377,7 +396,8 @@ int CoalescePendingMotionEvents(const XEvent* xev, XEvent* last_event) {
       // that's what the message pump would do. Device events come in pairs
       // with one from the master and one from the slave so there will
       // always be at least one pending.
-    if (!ui::TouchFactory::GetInstance()->ShouldProcessXI2Event(&next_event)) {
+      if (!ui::TouchFactory::GetInstance()->ShouldProcessXI2Event(
+              &next_event)) {
         XFreeEventData(display, &next_event.xcookie);
         XNextEvent(display, &next_event);
         continue;
@@ -418,8 +438,9 @@ int CoalescePendingMotionEvents(const XEvent* xev, XEvent* last_event) {
       XFreeEventData(display, &next_event.xcookie);
       break;
     }
+  }
 
-  if (event_type == XI_Motion && num_coalesced > 0)
+  if (is_motion && num_coalesced > 0)
     UMA_HISTOGRAM_COUNTS_10000("Event.CoalescedCount.Mouse", num_coalesced);
   return num_coalesced;
 }

ui/events/x/x11_event_translation.cc

@@ -12,6 +12,7 @@
 #include "ui/events/event_utils.h"
 #include "ui/events/keycodes/keyboard_code_conversion_x.h"
 #include "ui/events/pointer_details.h"
+#include "ui/events/types/event_type.h"
 #include "ui/events/x/events_x_utils.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/x/x11.h"

ui/platform_window/x11/x11_window.cc

@@ -91,12 +91,13 @@ ui::XWindow::Configuration ConvertInitPropertiesToXWindowConfig(
 
 // Coalesce touch/mouse events if needed
 bool CoalesceEventsIfNeeded(XEvent* const xev, EventType type, XEvent* out) {
-  if (xev->type != GenericEvent ||
-      (type != ui::ET_TOUCH_MOVED && type != ui::ET_MOUSE_MOVED &&
-       type != ui::ET_MOUSE_DRAGGED)) {
-    return false;
-  }
+  if (xev->type == MotionNotify ||
+      (xev->type == GenericEvent &&
+       (type == ui::ET_TOUCH_MOVED || type == ui::ET_MOUSE_MOVED ||
+        type == ui::ET_MOUSE_DRAGGED))) {
     return ui::CoalescePendingMotionEvents(xev, out) > 0;
+  }
+  return false;
 }
 
 }  // namespace