Add UseCounter on Event::stop{Immediate,}Propagation().

third_party/WebKit/Source/core/events/Event.idl

Index: third_party/WebKit/Source/core/events/Event.idl
diff --git a/third_party/WebKit/Source/core/events/Event.idl b/third_party/WebKit/Source/core/events/Event.idl
index 19c632680673b620d830ecb460a454fb9e49508d..82bd377fa19cda3096ef57f02af6efba1f170536 100644
--- a/third_party/WebKit/Source/core/events/Event.idl
+++ b/third_party/WebKit/Source/core/events/Event.idl
@@ -35,8 +35,8 @@
     const unsigned short BUBBLING_PHASE = 3;
     readonly attribute unsigned short eventPhase;
 
-    void stopPropagation();
-    void stopImmediatePropagation();
+    [Measure] void stopPropagation();
+    [Measure] void stopImmediatePropagation();
 
     readonly attribute boolean bubbles;
     readonly attribute boolean cancelable;