Add UseCounters for non-standard MouseEvent IDL attributes

Source/core/frame/UseCounter.h

Index: Source/core/frame/UseCounter.h
diff --git a/Source/core/frame/UseCounter.h b/Source/core/frame/UseCounter.h
index c61b6925ad62b56d9bf77b2b847bf09ae6b41f91..73165f17668edd7d6f2c90220b5ebb4dd21f57b9 100644
--- a/Source/core/frame/UseCounter.h
+++ b/Source/core/frame/UseCounter.h
@@ -489,6 +489,12 @@ public:
         HTMLTableCellElementChar = 499,
         HTMLTableCellElementCharOff = 500,
         SVGSMILElementInDocument = 501,
+        MouseEventOffsetX = 502,
+        MouseEventOffsetY = 503,
+        MouseEventX = 504,
+        MouseEventY = 505,
+        MouseEventFromElement = 506,
+        MouseEventToElement = 507,
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.
         // Also, run update_use_counter_feature_enum.py in chromium/src/tools/metrics/histograms/