Bug 898580 - Add nsIDOMWindowUtils.getViewId(element). r=smaug

dom/base/nsDOMWindowUtils.cpp

@@ -1694,6 +1694,16 @@ nsDOMWindowUtils::FindElementWithViewId(nsViewID aID,
   return content ? CallQueryInterface(content, aResult) : NS_OK;
 }
 
+NS_IMETHODIMP
+nsDOMWindowUtils::GetViewId(nsIDOMElement* aElement, nsViewID* aResult)
+{
+  nsCOMPtr<nsIContent> content = do_QueryInterface(aElement);
+  if (content && nsLayoutUtils::FindIDFor(content, aResult)) {
+    return NS_OK;
+  }
+  return NS_ERROR_NOT_AVAILABLE;
+}
+
 NS_IMETHODIMP
 nsDOMWindowUtils::GetScreenPixelsPerCSSPixel(float* aScreenPixels)
 {

dom/interfaces/base/nsIDOMWindowUtils.idl

@@ -42,7 +42,7 @@ interface nsIURI;
 interface nsIDOMEventTarget;
 interface nsIRunnable;
 
-[scriptable, uuid(ff1cec22-b183-40d3-8b42-b81a2f0ba4e6)]
+[scriptable, uuid(d6e733ef-492b-4e67-b723-28571c2959f0)]
 interface nsIDOMWindowUtils : nsISupports {
 
   /**
@@ -1177,6 +1177,12 @@ interface nsIDOMWindowUtils : nsISupports {
    */
   nsIDOMElement findElementWithViewId(in nsViewID aId);
 
+  /**
+   * Find the view ID for a given element. This is the reverse of
+   * findElementWithViewId().
+   */
+  nsViewID getViewId(in nsIDOMElement aElement);
+
   /**
    * Checks the layer tree for this window and returns true
    * if all layers have transforms that are translations by integers,