Add feature to enable media history store.

Bug: 997813
Change-Id: I88dfa13db52d2968f846d72015e99c84e9808c01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815543
Commit-Queue: Evan Liu <evliu@google.com>
Auto-Submit: Evan Liu <evliu@google.com>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710071}

media/base/media_switches.cc

@@ -327,6 +327,10 @@ const base::Feature kSpecCompliantCanPlayThrough{
 const base::Feature kUseNewMediaCache{"use-new-media-cache",
                                       base::FEATURE_ENABLED_BY_DEFAULT};
 
+// Enables using the media history store to store media engagement metrics.
+const base::Feature kUseMediaHistoryStore{"UseMediaHistoryStore",
+                                          base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Use R16 texture for 9-16 bit channel instead of half-float conversion by CPU.
 const base::Feature kUseR16Texture{"use-r16-texture",
                                    base::FEATURE_DISABLED_BY_DEFAULT};

media/base/media_switches.h

@@ -142,6 +142,7 @@ MEDIA_EXPORT extern const base::Feature kUnifiedAutoplay;
 MEDIA_EXPORT extern const base::Feature kUseAndroidOverlay;
 MEDIA_EXPORT extern const base::Feature kUseAndroidOverlayAggressively;
 MEDIA_EXPORT extern const base::Feature kUseFakeDeviceForMediaStream;
+MEDIA_EXPORT extern const base::Feature kUseMediaHistoryStore;
 MEDIA_EXPORT extern const base::Feature kUseNewMediaCache;
 MEDIA_EXPORT extern const base::Feature kUseR16Texture;
 MEDIA_EXPORT extern const base::Feature kUseSurfaceLayerForVideo;