Merge inbound to mozilla-central. a=merge

dom/base/AnonymousContent.cpp

@@ -197,5 +197,16 @@ void AnonymousContent::GetComputedStylePropertyValue(
   aRv = cs->GetPropertyValue(aPropertyName, aResult);
 }
 
+void AnonymousContent::GetTargetIdForEvent(Event& aEvent, DOMString& aResult)
+{
+  nsCOMPtr<Element> el = do_QueryInterface(aEvent.GetOriginalTarget());
+  if (el && el->IsInNativeAnonymousSubtree() && mContentNode->Contains(el)) {
+    aResult.SetKnownLiveAtom(el->GetID(), DOMString::eTreatNullAsNull);
+    return;
+  }
+
+  aResult.SetNull();
+}
+
 }  // namespace dom
 }  // namespace mozilla

dom/base/AnonymousContent.h

@@ -8,6 +8,7 @@
 #define mozilla_dom_AnonymousContent_h
 
 #include "mozilla/dom/Element.h"
+#include "mozilla/dom/Event.h"
 #include "nsCycleCollectionParticipant.h"
 #include "nsICSSDeclaration.h"
 #include "mozilla/dom/Document.h"
@@ -68,6 +69,8 @@ class AnonymousContent final {
                                      const nsAString& aPropertyName,
                                      DOMString& aResult, ErrorResult& aRv);
 
+  void GetTargetIdForEvent(Event& aEvent, DOMString& aResult);
+
  private:
   ~AnonymousContent();
   RefPtr<Element> mContentNode;

dom/webidl/AnonymousContent.webidl

@@ -85,4 +85,10 @@ interface AnonymousContent {
   [Throws]
   DOMString? getComputedStylePropertyValue(DOMString elementId,
                                            DOMString propertyName);
+
+  /**
+   * If event's original target is in the anonymous content, this returns the id
+   * attribute value of the target.
+   */
+  DOMString? getTargetIdForEvent(Event event);
 };