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

ui/base/events/event_utils.h

Index: ui/base/events/event_utils.h
diff --git a/ui/base/events/event_utils.h b/ui/base/events/event_utils.h
index 05ce2cd1135e701fd3c7af2f2518cd54c3f3fd76..4c73fe112c7babb6b05841df57b0142c0a040c77 100644
--- a/ui/base/events/event_utils.h
+++ b/ui/base/events/event_utils.h
@@ -68,6 +68,15 @@ UI_EXPORT KeyboardCode KeyboardCodeFromNative(
 // Returns true if the message is a mouse event.
 UI_EXPORT bool IsMouseEvent(const base::NativeEvent& native_event);
 
+// Returns true if |type| is a Key event type.
+UI_EXPORT bool IsKeyEventType(EventType type);
+
+// Returns true if |type| is a Mouse event type.
+UI_EXPORT bool IsMouseEventType(EventType type);
+
+// Returns true if |type| is a Touch event type.
+UI_EXPORT bool IsTouchEventType(EventType type);
+
 // Returns the flags of the button that changed during a press/release.
 UI_EXPORT int GetChangedMouseButtonFlagsFromNative(
     const base::NativeEvent& native_event);