Add Keyboard Latency UMA Metrics.

ui/events/event.cc

Index: ui/events/event.cc
diff --git a/ui/events/event.cc b/ui/events/event.cc
index 64f06d0cae3d0fbef8a52b7a4c723663beca8582..7483c6c10091c7cbbb5c9c0d855aa5742884d048 100644
--- a/ui/events/event.cc
+++ b/ui/events/event.cc
@@ -149,13 +149,18 @@ SourceEventType EventTypeToLatencySourceEventType(EventType type) {
     case ET_SCROLL_FLING_CANCEL:
       return SourceEventType::UNKNOWN;
 
+    case ui::ET_KEY_PRESSED:
+      return ui::SourceEventType::KEY;
+
     case ET_MOUSE_PRESSED:
     case ET_MOUSE_DRAGGED:
     case ET_MOUSE_RELEASED:
     case ET_MOUSE_MOVED:
     case ET_MOUSE_ENTERED:
     case ET_MOUSE_EXITED:
-    case ET_KEY_PRESSED:
+    // We measure latency for key presses, not key releases. Most behavior is

[mfomitchev, 2017/04/04 14:59:06]

Nit: Perhaps this comment should be in the SourceEventType enum? We can leave
something here as well.

[tdresser, 2017/05/01 15:49:21]

Added a comment in SourceEventType enum.

+    // keyed off of presses, and release latency is higher than press latency as
+    // it's impacted by event handling of the press event.
     case ET_KEY_RELEASED:
     case ET_MOUSE_CAPTURE_CHANGED:
     case ET_DROP_TARGET_EVENT:
@@ -1140,6 +1145,11 @@ KeyEvent::KeyEvent(const base::NativeEvent& native_event, int event_flags)
       key_code_(KeyboardCodeFromNative(native_event)),
       code_(CodeFromNative(native_event)),
       is_char_(IsCharFromNative(native_event)) {
+  latency()->AddLatencyNumberWithTimestamp(
+      INPUT_EVENT_LATENCY_ORIGINAL_COMPONENT, 0, 0,
+      base::TimeTicks::FromInternalValue(time_stamp().ToInternalValue()), 1);
+  latency()->AddLatencyNumber(INPUT_EVENT_LATENCY_UI_COMPONENT, 0, 0);
+
   if (IsRepeated(*this))
     set_flags(flags() | ui::EF_IS_REPEAT);