Add UseCounters for UIEvent.charCode/keyCode/which

These belong on the KeyboardEvent interface, so add them to
KeyboardEvent.idl and count anything that still falls back to UIEvent.

MouseEvent.which does not appear to be in any spec, but it is supported
by most browsers. Measure its usage to help determine its future.

Review URL: https://codereview.chromium.org/725073003

git-svn-id: svn://svn.chromium.org/blink/trunk@185393 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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

@@ -48,5 +48,8 @@
                            [Default=Undefined] optional boolean altKey,
                            [Default=Undefined] optional boolean shiftKey,
                            [Default=Undefined] optional boolean metaKey);
-};
 
+    readonly attribute long charCode;
+    readonly attribute long keyCode;
+    readonly attribute long which;
+};

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

@@ -58,6 +58,7 @@
     [MeasureAs=MouseEventY] readonly attribute long y;
     [MeasureAs=MouseEventFromElement] readonly attribute Node fromElement;
     [MeasureAs=MouseEventToElement] readonly attribute Node toElement;
+    [MeasureAs=MouseEventWhich] readonly attribute long which;
 
     // FIXME: this belongs on the DragEvent interface
     readonly attribute DataTransfer dataTransfer;

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

@@ -36,7 +36,7 @@
     [MeasureAs=UIEventPageY] readonly attribute long pageY;
 
     // FIXME: these belong on the KeyboardEvent interface
-    readonly attribute long keyCode;
-    readonly attribute long charCode;
-    readonly attribute long which;
+    [MeasureAs=UIEventCharCode] readonly attribute long charCode;
+    [MeasureAs=UIEventKeyCode] readonly attribute long keyCode;
+    [MeasureAs=UIEventWhich] readonly attribute long which;
 };

third_party/WebKit/Source/core/frame/UseCounter.h

@@ -561,6 +561,10 @@ public:
 
         SetReferrerPolicy = 593,
         DOMImplementationHasFeatureReturnFalseInternal = 594,
+        MouseEventWhich = 595,
+        UIEventCharCode = 596,
+        UIEventKeyCode = 597,
+        UIEventWhich = 598,
 
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.