Bug 968923 - part 5b - add nsIDOMWindowUtils::forceUseCounterFlush; r=bz

Use counter submission normally happens at document destruction.  For
testing use counters, however, we need to have use counters updated in
telemetry at deterministic points.  Therefore, we provide a method on
nsIDOMWindowUtils that forces use counters out to telemetry so we can
examine them.

dom/html/HTMLImageElement.cpp

@@ -11,6 +11,7 @@
 #include "nsPresContext.h"
 #include "nsMappedAttributes.h"
 #include "nsSize.h"
+#include "nsDocument.h"
 #include "nsIDocument.h"
 #include "nsIDOMMutationEvent.h"
 #include "nsIScriptContext.h"
@@ -27,6 +28,7 @@
 #include "mozilla/dom/HTMLFormElement.h"
 #include "nsAttrValueOrString.h"
 #include "imgLoader.h"
+#include "Image.h"
 
 // Responsive images!
 #include "mozilla/dom/HTMLSourceElement.h"
@@ -1301,6 +1303,18 @@ HTMLImageElement::MediaFeatureValuesChanged()
   QueueImageLoadTask();
 }
 
+void
+HTMLImageElement::FlushUseCounters()
+{
+  nsCOMPtr<imgIRequest> request;
+  GetRequest(CURRENT_REQUEST, getter_AddRefs(request));
+
+  nsCOMPtr<imgIContainer> container;
+  request->GetImage(getter_AddRefs(container));
+
+  static_cast<image::Image*>(container.get())->ReportUseCounters();
+}
+
 } // namespace dom
 } // namespace mozilla