Add kExposeSwDecodersToWebRTC media switch.

Instead of having kUseDecoderStreamForWebRTC gate both HW/SW fallback decoding and exposing SW decoders to WebRTC directly, add this switch for more fine grained control.

(cherry picked from commit 34d7d9a)

Bug: chromium:1173503
Change-Id: If4b1c1242935c7ca1f01772fbdd310587b60da81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2721726
Commit-Queue: Philip Eliasson <philipel@chromium.org>
Reviewed-by: Frank Liberato <liberato@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#858947}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2735054
Cr-Commit-Position: refs/branch-heads/4430@{#241}
Cr-Branched-From: e5ce7dc-refs/heads/master@{#857950}

media/base/media_switches.cc

@@ -280,6 +280,11 @@ const base::Feature kUseAndroidOverlayAggressively{
 const base::Feature kUseDecoderStreamForWebRTC{
     "UseDecoderStreamForWebRTC", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// If enabled, when RTCVideoDecoderAdapter is used then SW decoders will be
+// exposed directly to WebRTC.
+const base::Feature kExposeSwDecodersToWebRTC{
+    "ExposeSwDecodersToWebRTC", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Let video without audio be paused when it is playing in the background.
 const base::Feature kBackgroundVideoPauseOptimization{
     "BackgroundVideoPauseOptimization", base::FEATURE_ENABLED_BY_DEFAULT};

media/base/media_switches.h

@@ -122,6 +122,7 @@ MEDIA_EXPORT extern const base::Feature kD3D11VideoDecoderSkipMultithreaded;
 MEDIA_EXPORT extern const base::Feature kD3D11VideoDecoderAlwaysCopy;
 MEDIA_EXPORT extern const base::Feature kD3D11VideoDecoderAllowOverlay;
 MEDIA_EXPORT extern const base::Feature kEnableMediaInternals;
+MEDIA_EXPORT extern const base::Feature kExposeSwDecodersToWebRTC;
 MEDIA_EXPORT extern const base::Feature kExternalClearKeyForTesting;
 MEDIA_EXPORT extern const base::Feature kFFmpegDecodeOpaqueVP8;
 MEDIA_EXPORT extern const base::Feature kFailUrlProvisionFetcherForTesting;

media/renderers/default_decoder_factory.cc

@@ -109,6 +109,9 @@ DefaultDecoderFactory::GetSupportedVideoDecoderConfigsForWebRTC() {
   }
 #endif
 
+  if (!base::FeatureList::IsEnabled(media::kExposeSwDecodersToWebRTC))
+    return supported_configs;
+
 #if BUILDFLAG(ENABLE_LIBVPX)
   SupportedVideoDecoderConfigs vpx_configs =
       VpxVideoDecoder::SupportedConfigs();