bug 1242268 store a node type string pointer on engines and use that for memory reporting r=padenot

removing some off-main-thread usage of AudioNodeEngine::mNode.

MozReview-Commit-ID: GYgFzPJQjjm

--HG--
extra : rebase_source : 9c4697b27bdfee971d9502c4b0573cdb7c740774

dom/media/webaudio/AudioNodeEngine.h

@@ -257,6 +257,7 @@ public:
 
   explicit AudioNodeEngine(dom::AudioNode* aNode)
     : mNode(aNode)
+    , mNodeType(aNode ? aNode->NodeType() : nullptr)
     , mInputCount(aNode ? aNode->NumberOfInputs() : 1)
     , mOutputCount(aNode ? aNode->NumberOfOutputs() : 0)
   {
@@ -394,14 +395,15 @@ public:
                            AudioNodeSizes& aUsage) const
   {
     aUsage.mEngine = SizeOfIncludingThis(aMallocSizeOf);
+    aUsage.mNodeType = mNodeType;
     if (mNode) {
       aUsage.mDomNode = mNode->SizeOfIncludingThis(aMallocSizeOf);
-      aUsage.mNodeType = mNode->NodeType();
     }
   }
 
 private:
   dom::AudioNode* mNode;
+  const char* const mNodeType;
   const uint16_t mInputCount;
   const uint16_t mOutputCount;
 };