bug 1270916 - make TreeMutation track if it should be queueing events r=davidb

Soon we will want to know if events should be emitted independt of EventTrees.

accessible/base/EventTree.cpp

@@ -25,7 +25,8 @@ EventTree* const TreeMutation::kNoEventTree = reinterpret_cast<EventTree*>(-1);
 TreeMutation::TreeMutation(Accessible* aParent, bool aNoEvents) :
   mParent(aParent), mStartIdx(UINT32_MAX),
   mStateFlagsCopy(mParent->mStateFlags),
-  mEventTree(aNoEvents ? kNoEventTree : nullptr)
+  mEventTree(aNoEvents ? kNoEventTree : nullptr),
+  mQueueEvents(!aNoEvents)
 {
 #ifdef DEBUG
   mIsDone = false;

accessible/base/EventTree.h

@@ -49,6 +49,11 @@ private:
   uint32_t mStateFlagsCopy;
   EventTree* mEventTree;
 
+  /*
+   * True if mutation events should be queued.
+   */
+  bool mQueueEvents;
+
 #ifdef DEBUG
   bool mIsDone;
 #endif