Add a UseCounter for the webkitallowfullscreen attribute

Source/core/dom/FullscreenElementStack.cpp

Index: Source/core/dom/FullscreenElementStack.cpp
diff --git a/Source/core/dom/FullscreenElementStack.cpp b/Source/core/dom/FullscreenElementStack.cpp
index 2f72ac811d85fb537842fe0cb8faf66730c4b3fd..8fb5ebceaff45fd9e99583562649b08a5d3600e1 100644
--- a/Source/core/dom/FullscreenElementStack.cpp
+++ b/Source/core/dom/FullscreenElementStack.cpp
@@ -34,6 +34,7 @@
 #include "core/frame/FrameHost.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
+#include "core/frame/UseCounter.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/html/HTMLMediaElement.h"
 #include "core/page/Chrome.h"
@@ -45,13 +46,18 @@ namespace WebCore {
 
 using namespace HTMLNames;
 
-static bool isAttributeOnAllOwners(const WebCore::QualifiedName& attribute, const WebCore::QualifiedName& prefixedAttribute, const HTMLFrameOwnerElement* owner)
+static bool fullscreenIsAllowedForAllOwners(const Document& document)
 {
+    const HTMLFrameOwnerElement* owner = document.ownerElement();
     if (!owner)
         return true;
     do {
-        if (!(owner->hasAttribute(attribute) || owner->hasAttribute(prefixedAttribute)))
-            return false;
+        if (!owner->hasAttribute(allowfullscreenAttr)) {
+            if (owner->hasAttribute(webkitallowfullscreenAttr))
+                UseCounter::count(document, UseCounter::PrefixedAllowFullscreenAttribute);
+            else
+                return false;
+        }
     } while ((owner = owner->document().ownerElement()));
     return true;
 }
@@ -134,7 +140,7 @@ void FullscreenElementStack::documentWasDisposed()
 bool FullscreenElementStack::fullScreenIsAllowedForElement(Element* element) const
 {
     ASSERT(element);
-    return isAttributeOnAllOwners(allowfullscreenAttr, webkitallowfullscreenAttr, element->document().ownerElement());
+    return fullscreenIsAllowedForAllOwners(element->document());
 }
 
 void FullscreenElementStack::requestFullScreenForElement(Element* element, unsigned short flags, FullScreenCheckType checkType)
@@ -359,8 +365,7 @@ bool FullscreenElementStack::webkitFullscreenEnabled(Document& document)
     // browsing context's documents have their fullscreen enabled flag set, or false otherwise.
 
     // Top-level browsing contexts are implied to have their allowFullScreen attribute set.
-    return isAttributeOnAllOwners(allowfullscreenAttr, webkitallowfullscreenAttr, document.ownerElement());
-
+    return fullscreenIsAllowedForAllOwners(document);
 }
 
 void FullscreenElementStack::webkitWillEnterFullScreenForElement(Element* element)