Bug 1429284 - Expose compositor dropped frame count to HTMLMediaElement's debug info. r=jwwang

MozReview-Commit-ID: GYtHxdsGSk1

--HG--
extra : rebase_source : 2ba90d5899c2a268879722476da81e9a07b83a88

dom/html/HTMLMediaElement.cpp

@@ -1585,6 +1585,11 @@ HTMLMediaElement::MozRequestDebugInfo(ErrorResult& aRv)
   nsAutoString result;
   GetMozDebugReaderData(result);
 
+  if (mVideoFrameContainer) {
+    result.AppendPrintf("Compositor dropped frame(including when element's invisible): %u\n",
+                        mVideoFrameContainer->GetDroppedImageCount());
+  }
+
   if (mMediaKeys) {
     nsString EMEInfo;
     GetEMEInfo(EMEInfo);