Bug 1330243 - add preference to enable rust mp4 parser. r=kinetik

MozReview-Commit-ID: LINNEMiXYx4

--HG--
extra : rebase_source : 747b9854b0d5d1f0419c59c5966414872e8ea158

dom/media/MediaPrefs.h

@@ -170,6 +170,8 @@ private:
   DECL_MEDIA_PREF("media.rust.test_mode",                     RustTestMode, bool, false);
 #endif
 
+  DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, false);
+
 public:
   // Manage the singleton:
   static MediaPrefs& GetSingleton();

media/libstagefright/binding/MP4Metadata.cpp

@@ -230,7 +230,7 @@ IndiceWrapperRust::GetIndice(size_t aIndex, Index::Indice& aIndice) const
 MP4Metadata::MP4Metadata(Stream* aSource)
  : mStagefright(MakeUnique<MP4MetadataStagefright>(aSource))
  , mRust(MakeUnique<MP4MetadataRust>(aSource))
- , mPreferRust(false)
+ , mPreferRust(MediaPrefs::EnableRustMP4Parser())
  , mReportedAudioTrackTelemetry(false)
  , mReportedVideoTrackTelemetry(false)
 #ifndef RELEASE_OR_BETA