Add Keyboard Latency UMA Metrics.

chrome/browser/chromeos/accessibility/event_handler_common.cc

Index: chrome/browser/chromeos/accessibility/event_handler_common.cc
diff --git a/chrome/browser/chromeos/accessibility/event_handler_common.cc b/chrome/browser/chromeos/accessibility/event_handler_common.cc
index d1da17a19bf501dfe16995569783a34281ea51a8..efadb10be079cad973843ff78dd3c122163bbfd1 100644
--- a/chrome/browser/chromeos/accessibility/event_handler_common.cc
+++ b/chrome/browser/chromeos/accessibility/event_handler_common.cc
@@ -49,6 +49,7 @@ void ForwardKeyToExtension(const ui::KeyEvent& key_event,
   }
 
   const content::NativeWebKeyboardEvent web_event(key_event);
+  // Don't forward latency info, as these are getting forwarded to an extension.
   rvh->GetWidget()->ForwardKeyboardEvent(web_event);
 }
 }  // namespace chromeos