Bug 1346116 part 1 - initialize MediaDecoder::mIsDocumentVisible and MediaDecoder::mIsElementVisible at HTMLMediaElement::FinishDecoderSetup(); r=jwwang

Initialize the MediaDecoder::mIsElementVisible to be "!aOwner->IsHidden()" at the MediaDecoder's constructor is wrong.
Insted, we initialize both MediaDecoder::mIsDocumentVisible and MediaDecoder::mIsElementVisible to be false at the construtor,
and then assign the HTMLMediaElement's real values to them at HTMLMediaElement::FinishDecoderSetup() via the the MediaDecoder::SetActiviyChangesToDecoder().

The initialization values of MediaDecoder::mIsDocumentVisible and MediaDecoder::mIsElementVisible (in the constructor) do not matter because the valuse are
not read untile the first MediaDecoder::SetActiviyChangesToDecoder() method call.

MozReview-Commit-ID: Cdovq5pG9Nv

--HG--
extra : rebase_source : 91f3b4c2515124b4c195dd246bd9b404178a35de
extra : source : 81b5e89a5bd20f37b8c3daa1230db30808026ff4

dom/html/HTMLMediaElement.cpp

@@ -4713,6 +4713,8 @@ nsresult HTMLMediaElement::FinishDecoderSetup(MediaDecoder* aDecoder,
   }
   // Notify the decoder of suspend taint.
   mDecoder->SetSuspendTaint(mHasSuspendTaint);
+  // Notify the decoder of the initial activity status.
+  NotifyDecoderActivityChanges();
 
   // Update decoder principal before we start decoding, since it
   // can affect how we feed data to MediaStreams

dom/media/MediaDecoder.cpp

@@ -395,8 +395,8 @@ MediaDecoder::MediaDecoder(MediaDecoderOwner* aOwner)
   , mMinimizePreroll(false)
   , mMediaTracksConstructed(false)
   , mFiredMetadataLoaded(false)
-  , mIsDocumentVisible(!aOwner->IsHidden())
-  , mIsElementVisible(!aOwner->IsHidden())
+  , mIsDocumentVisible(false)
+  , mIsElementVisible(false)
   , mForcedHidden(false)
   , mHasSuspendTaint(false)
   , INIT_MIRROR(mStateMachineIsShutdown, true)