Bug 1309142. Part 2 - add StateObject::HandleShutdown(). r=JamesCheng

MozReview-Commit-ID: 64VPA1fxLzF

--HG--
extra : rebase_source : 271d75f4766dda88b2da68db6061cafda1e76295
extra : source : 3f62381eb06918fb2e591c245e96c519967cc59b

dom/media/MediaDecoderStateMachine.cpp

@@ -214,6 +214,8 @@ public:
 
   virtual bool HandleAudioCaptured() { return false; }
 
+  virtual RefPtr<ShutdownPromise> HandleShutdown();
+
   virtual void DumpDebugInfo() {}
 
 protected:
@@ -885,6 +887,12 @@ public:
     MOZ_DIAGNOSTIC_ASSERT(false, "Can't seek in shutdown state.");
     return MediaDecoder::SeekPromise::CreateAndReject(true, __func__);
   }
+
+  RefPtr<ShutdownPromise> HandleShutdown() override
+  {
+    MOZ_DIAGNOSTIC_ASSERT(false, "Already shutting down.");
+    return nullptr;
+  }
 };
 
 bool
@@ -906,6 +914,20 @@ StateObject::HandleDormant(bool aDormant)
   return true;
 }
 
+RefPtr<ShutdownPromise>
+MediaDecoderStateMachine::
+StateObject::HandleShutdown()
+{
+  auto master = mMaster;
+  SetState<ShutdownState>();
+
+  return master->mReader->Shutdown()
+    ->Then(master->OwnerThread(), __func__, master,
+           &MediaDecoderStateMachine::FinishShutdown,
+           &MediaDecoderStateMachine::FinishShutdown)
+    ->CompletionPromise();
+}
+
 void
 MediaDecoderStateMachine::
 DecodeMetadataState::OnMetadataRead(MetadataHolder* aMetadata)
@@ -2144,16 +2166,7 @@ RefPtr<ShutdownPromise>
 MediaDecoderStateMachine::Shutdown()
 {
   MOZ_ASSERT(OnTaskQueue());
-
+  return mStateObj->HandleShutdown();
-  mStateObj->SetState<ShutdownState>();
-
-  // Put a task in the decode queue to shutdown the reader.
-  // the queue to spin down.
-  return mReader->Shutdown()
-    ->Then(OwnerThread(), __func__, this,
-           &MediaDecoderStateMachine::FinishShutdown,
-           &MediaDecoderStateMachine::FinishShutdown)
-    ->CompletionPromise();
 }
 
 void MediaDecoderStateMachine::PlayStateChanged()