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..470fa22149dad869c8976cc16f7f5ed603d22eb7 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 +630,24 @@ int CoalescePendingMotionEvents(const XEvent* xev,
     }
     break;
   }
+  if (num_coalesed > 0) {
+    base::TimeDelta delta = ui::EventTimeFromNative(last_event) -
+        ui::EventTimeFromNative(const_cast<XEvent*>(xev));
+    ui::EventType ui_type = ui::EventTypeFromNative(const_cast<XEvent*>(xev));
+    if (ui::IsMouseEventType(ui_type)) {
+      UMA_HISTOGRAM_COUNTS_10000("Event.CoalescedCount.Mouse", num_coalesed);
+      UMA_HISTOGRAM_CUSTOM_COUNTS("Event.CoalescedLatency.Mouse",
+          delta.InMicroseconds(), 0, 1000000, 100);

[Rick Byers, 2013/04/05 19:32:24]

For these times I think microseconds is overkill.  We receive touch events at
100hz on pixel.  I'd suggest just using UMA_HISTOGRAM_TIMES to simplify this
even further.

[varunjain, 2013/04/05 22:04:07]

Done.

+    } else if (ui::IsTouchEventType(ui_type)) {
+      UMA_HISTOGRAM_COUNTS_10000("Event.CoalescedCount.Touch", num_coalesed);
+      UMA_HISTOGRAM_CUSTOM_COUNTS("Event.CoalescedLatency.Touch",
+          delta.InMicroseconds(), 0, 1000000, 100);
+    } else {
+      UMA_HISTOGRAM_COUNTS_10000("Event.CoalescedCount.Other", num_coalesed);
+      UMA_HISTOGRAM_CUSTOM_COUNTS("Event.CoalescedLatency.Other",
+          delta.InMicroseconds(), 0, 1000000, 100);
+    }
+  }
   return num_coalesed;
 }
 #endif