Bug 1328547. part 3 - inline NeedToDecode{Audio,Video} and remove some checks. r=kaku

1. |mState != DECODER_STATE_SEEKING| is true in DecodingState.
2. mSentFirstFrameLoadedEvent is true in DecodingState.
3. mMinimizePreroll is false because pop events fire only after MDSM starts playing.

MozReview-Commit-ID: FTkXmtEnzY5

--HG--
extra : rebase_source : 30392be881ebdb96469189a584a57b89d60cc2b4

dom/media/MediaDecoderStateMachine.cpp

@@ -1998,13 +1998,13 @@ DecodingState::Enter()
 
   mOnAudioPopped = AudioQueue().PopEvent().Connect(
     OwnerThread(), [this] () {
-    if (mMaster->NeedToDecodeAudio()) {
+    if (mMaster->IsAudioDecoding() && !mMaster->HaveEnoughDecodedAudio()) {
       mMaster->EnsureAudioDecodeTaskQueued();
     }
   });
   mOnVideoPopped = VideoQueue().PopEvent().Connect(
     OwnerThread(), [this] () {
-    if (mMaster->NeedToDecodeVideo()) {
+    if (mMaster->IsVideoDecoding() && !mMaster->HaveEnoughDecodedVideo()) {
       mMaster->EnsureVideoDecodeTaskQueued();
     }
   });