Add VP9 Hardware Decoding with DXVA (Non-MFT), Vista+

Thanks to Maggie (imjustsomeoneiguess) on discord for helping with a lot of this VP9 media code.
This is the first browser so far to support VP9 Non MFT

dom/media/platforms/wmf/WMFVideoMFTManager.cpp

@@ -314,6 +314,28 @@ FindD3D9BlacklistedDLL() {
                                 "media.wmf.disable-d3d9-for-dlls");
 }
 
+DXVA2Manager*
+WMFVideoMFTManager::CreateVP9DXVA(layers::KnowsCompositor* aCompositor,
+                                  nsACString& aFailureReason, const GUID& aGUID)
+{
+  DXVA2Manager* result = nullptr;
+  nsCOMPtr<nsIRunnable> event = NS_NewRunnableFunction([&]() {
+    const nsCString& blocked = FindD3D9BlacklistedDLL();
+    if (!blocked.IsEmpty()) {
+      aFailureReason.AssignLiteral("D3D9 DLL is blocklisted");
+      return;
+    }
+    result = DXVA2Manager::CreateD3D9DXVA(aCompositor, aFailureReason, &aGUID);
+  });
+  if (NS_IsMainThread()) {
+    event->Run();
+  } else {
+    nsCOMPtr<nsIThread> mainThread = do_GetMainThread();
+    SyncRunnable::DispatchToThread(mainThread, event);
+  }
+  return result;
+}
+
 class CreateDXVAManagerEvent : public Runnable {
 public:
   CreateDXVAManagerEvent(LayersBackend aBackend,