Bug 1299064. Part 1 - move |SetState(nextState)| and ScheduleStateMachine() to the bottom of SeekCompleted(). r=kaku

UpdatePlaybackPositionInternal(), |mQuickBuffering = false| and |mMediaSink->Redraw| should belong to
the exit action of SEEKING. By change the order of the statements, we have a better definition/scope
for the jobs of each state.

MozReview-Commit-ID: 6WESdwaD8Ba

--HG--
extra : rebase_source : eab747abcf2cf375ed99d5800eba9c5558e1436c

dom/media/MediaDecoderStateMachine.cpp

@@ -2181,12 +2181,6 @@ MediaDecoderStateMachine::SeekCompleted()
     FinishDecodeFirstFrame();
   }
 
-  if (nextState == DECODER_STATE_DECODING) {
-    SetState(DECODER_STATE_DECODING);
-  } else {
-    SetState(nextState);
-  }
-
   // Ensure timestamps are up to date.
   UpdatePlaybackPositionInternal(newCurrentTime);
 
@@ -2198,12 +2192,18 @@ MediaDecoderStateMachine::SeekCompleted()
   // if we need to buffer after the seek.
   mQuickBuffering = false;
 
-  ScheduleStateMachine();
-
   if (video) {
     mMediaSink->Redraw(mInfo.mVideo);
     mOnPlaybackEvent.Notify(MediaEventType::Invalidate);
   }
+
+  if (nextState == DECODER_STATE_DECODING) {
+    SetState(DECODER_STATE_DECODING);
+  } else {
+    SetState(nextState);
+  }
+
+  ScheduleStateMachine();
 }
 
 RefPtr<ShutdownPromise>