Bug 1208349 - Ensure we query PDM whether it supports MP4 before assuming it supports MP4. r=jya

dom/media/fmp4/MP4Decoder.cpp

@@ -275,7 +275,7 @@ CreateTestH264Decoder(layers::LayersBackend aBackend,
   PlatformDecoderModule::Init();
 
   nsRefPtr<PlatformDecoderModule> platform = PlatformDecoderModule::Create();
-  if (!platform) {
+  if (!platform || !platform->SupportsMimeType(NS_LITERAL_CSTRING("video/mp4"))) {
     return nullptr;
   }
 
@@ -331,7 +331,7 @@ CreateTestAACDecoder(AudioInfo& aConfig)
   PlatformDecoderModule::Init();
 
   nsRefPtr<PlatformDecoderModule> platform = PlatformDecoderModule::Create();
-  if (!platform) {
+  if (!platform || !platform->SupportsMimeType(NS_LITERAL_CSTRING("audio/mp4a-latm"))) {
     return nullptr;
   }