media/gpu/vaapi: Disable VA-API Low Power Encoder by default

As stated in https://crbug.com/929849#c58, there may be a risk to enable low
power encoder by default. We should perform A/B test via finch. This CL
disables the feature by default, which follows chrome feature release procedure.

Bug: 929849
Test: Confirm EncSliceLP is not used in appr.tc on sarien
Change-Id: I34638d0490d20746cbd630c5cc7bbc8c647b75f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1545437
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646650}

media/base/media_switches.cc

@@ -303,6 +303,10 @@ const base::Feature kUnifiedAutoplay{"UnifiedAutoplay",
 const base::Feature kUseSurfaceLayerForVideo{"UseSurfaceLayerForVideo",
                                              base::FEATURE_ENABLED_BY_DEFAULT};
 
+// Enable VA-API hardware low power encoder for all codecs.
+const base::Feature kVaapiLowPowerEncoder{"VaapiLowPowerEncoder",
+                                          base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enable VA-API hardware encode acceleration for VP8.
 const base::Feature kVaapiVP8Encoder{"VaapiVP8Encoder",
                                      base::FEATURE_ENABLED_BY_DEFAULT};

media/base/media_switches.h

@@ -133,6 +133,7 @@ MEDIA_EXPORT extern const base::Feature kUseModernMediaControls;
 MEDIA_EXPORT extern const base::Feature kUseNewMediaCache;
 MEDIA_EXPORT extern const base::Feature kUseR16Texture;
 MEDIA_EXPORT extern const base::Feature kUseSurfaceLayerForVideo;
+MEDIA_EXPORT extern const base::Feature kVaapiLowPowerEncoder;
 MEDIA_EXPORT extern const base::Feature kVaapiVP8Encoder;
 MEDIA_EXPORT extern const base::Feature kVaapiVP9Encoder;
 MEDIA_EXPORT extern const base::Feature kVideoBlitColorAccuracy;

media/gpu/vaapi/vaapi_wrapper.cc

@@ -1690,7 +1690,8 @@ bool VaapiWrapper::Initialize(CodecMode mode, VAProfile va_profile) {
   std::vector<VAConfigAttrib> required_attribs =
       GetRequiredAttribs(mode, va_profile);
 
-  if ((mode == CodecMode::kEncode) && IsLowPowerEncSupported(va_profile)) {
+  if (mode == CodecMode::kEncode && IsLowPowerEncSupported(va_profile) &&
+      base::FeatureList::IsEnabled(kVaapiLowPowerEncoder)) {
     entrypoint = VAEntrypointEncSliceLP;
     DVLOG(2) << "Enable VA-API Low-Power Encode Entrypoint";
   }