linux_aura: Fix tab dragging performance.

ui/base/x/x11_util.h

Index: ui/base/x/x11_util.h
diff --git a/ui/base/x/x11_util.h b/ui/base/x/x11_util.h
index b1a6e4d82c9d417861fe51bcbf66f50fb58c8717..0b6653f645012bea1dec76b0feb78cc584e621ad 100644
--- a/ui/base/x/x11_util.h
+++ b/ui/base/x/x11_util.h
@@ -305,6 +305,12 @@ UI_EXPORT bool IsX11WindowFullScreen(XID window);
 // Return true if event type is MotionNotify.
 UI_EXPORT bool IsMotionEvent(XEvent* event);
 
+// Coalesce all pending motion events (touch or mouse) that are at the top of
+// the queue, and return the number eliminated, storing the last one in
+// |last_event|.
+UI_EXPORT int CoalescePendingMotionEvents(const XEvent* xev,
+                                          XEvent* last_event);
+
 // Returns the mapped button.
 int GetMappedButton(int button);