Add UMA metrics for measuring number of coalesed events and their latency.

ui/base/x/x11_util.cc

Index: ui/base/x/x11_util.cc
diff --git a/ui/base/x/x11_util.cc b/ui/base/x/x11_util.cc
index da03cd17a80b0c2b77a34119313345ee5059f76d..af5e402bb7d2ca4b2f94fc570d0f8fd004231791 100644
--- a/ui/base/x/x11_util.cc
+++ b/ui/base/x/x11_util.cc
@@ -28,6 +28,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
 #include "base/message_loop.h"
+#include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
@@ -629,6 +630,21 @@ int CoalescePendingMotionEvents(const XEvent* xev,
     }
     break;
   }
+
+  if (num_coalesed > 0) {
+    base::TimeDelta delta = ui::EventTimeFromNative(last_event) -
+        ui::EventTimeFromNative(const_cast<XEvent*>(xev));
+    if (event_type == XI_Motion) {
+      UMA_HISTOGRAM_COUNTS_10000("Event.CoalescedCount.Mouse", num_coalesed);
+      UMA_HISTOGRAM_TIMES("Event.CoalescedLatency.Mouse", delta);
+    } else {
+#if defined(USE_XI2_MT)
+      DCHECK(event_type == XI_TouchUpdate);

[sadrul, 2013/04/05 23:27:09]

DCHECK_EQ

[varunjain, 2013/04/08 14:37:12]

Done.

+#endif
+      UMA_HISTOGRAM_COUNTS_10000("Event.CoalescedCount.Touch", num_coalesed);
+      UMA_HISTOGRAM_TIMES("Event.CoalescedLatency.Touch", delta);
+    }
+  }
   return num_coalesed;
 }
 #endif