Add UseCounters for ViewportAPI

third_party/WebKit/Source/core/frame/VisualViewport.idl

Index: third_party/WebKit/Source/core/frame/VisualViewport.idl
diff --git a/third_party/WebKit/Source/core/frame/VisualViewport.idl b/third_party/WebKit/Source/core/frame/VisualViewport.idl
index 0f2f65fa5df18a3cf5c62c4e815286d61a0ef3b6..922befec33d05e4d6b058913ab8c36e2f9f9003e 100644
--- a/third_party/WebKit/Source/core/frame/VisualViewport.idl
+++ b/third_party/WebKit/Source/core/frame/VisualViewport.idl
@@ -30,16 +30,16 @@
     RuntimeEnabled=VisualViewportAPI,
     ImplementedAs=DOMVisualViewport,
 ] interface VisualViewport : EventTarget {
-    readonly attribute double scrollLeft;
-    readonly attribute double scrollTop;
+    [Measure] readonly attribute double scrollLeft;
+    [Measure] readonly attribute double scrollTop;
 
-    readonly attribute double pageX;
-    readonly attribute double pageY;
+    [Measure] readonly attribute double pageX;
+    [Measure] readonly attribute double pageY;
 
-    readonly attribute double clientWidth;
-    readonly attribute double clientHeight;
+    [Measure] readonly attribute double clientWidth;
+    [Measure] readonly attribute double clientHeight;
 
-    readonly attribute double scale;
+    [Measure] readonly attribute double scale;
 
     attribute EventHandler onresize;
     attribute EventHandler onscroll;