[Global Media Controls] Add feature flag for hardware key handling

This CL adds a feature flag to toggle hardware key handling. This
is currently unused and disabled by default.

Bug: 902792
Change-Id: Ic1dfd70a81f6aa7abb8fd79b504b0d3bd05843e3
Reviewed-on: https://chromium-review.googlesource.com/c/1323798Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606207}

media/base/media_switches.cc

@@ -353,6 +353,10 @@ const base::Feature kExternalClearKeyForTesting{
 const base::Feature kHardwareSecureDecryption{
     "HardwareSecureDecryption", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enables handling of hardware media keys for controlling media.
+const base::Feature kHardwareMediaKeyHandling{
+    "HardwareMediaKeyHandling", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Limits number of media tags loading in parallel to 6. This speeds up
 // preloading of any media that requires multiple requests to preload.
 const base::Feature kLimitParallelMediaPreloading{

media/base/media_switches.h

@@ -109,6 +109,7 @@ MEDIA_EXPORT extern const base::Feature kD3D11VP9Decoder;
 MEDIA_EXPORT extern const base::Feature kD3D11VideoDecoder;
 MEDIA_EXPORT extern const base::Feature kExternalClearKeyForTesting;
 MEDIA_EXPORT extern const base::Feature kFallbackAfterDecodeError;
+MEDIA_EXPORT extern const base::Feature kHardwareMediaKeyHandling;
 MEDIA_EXPORT extern const base::Feature kHardwareSecureDecryption;
 MEDIA_EXPORT extern const base::Feature kLimitParallelMediaPreloading;
 MEDIA_EXPORT extern const base::Feature kLowDelayVideoRenderingOnLiveStream;