GMC: Enable Picture in picture by default

This CL enables picture in picture in the Global Media Controls by
default on Windows, Mac, and Linux, since we've launched the feature.

Bug: 1071962
Change-Id: Ic8e26af8453d07211e3f96fac05c3c9aa5d32215
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2154918
Auto-Submit: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760224}

media/base/media_switches.cc

@@ -366,7 +366,14 @@ const base::Feature kGlobalMediaControlsOverlayControls{
 
 // Show picture-in-picture button in Global Media Controls.
 const base::Feature kGlobalMediaControlsPictureInPicture{
-    "GlobalMediaControlsPictureInPicture", base::FEATURE_DISABLED_BY_DEFAULT};
+  "GlobalMediaControlsPictureInPicture",
+#if defined(OS_WIN) || defined(OS_MACOSX) || \
+    (defined(OS_LINUX) && !defined(OS_CHROMEOS))
+      base::FEATURE_ENABLED_BY_DEFAULT
+#else
+      base::FEATURE_DISABLED_BY_DEFAULT
+#endif
+};
 
 // Enable new cpu load estimator. Intended for evaluation in local
 // testing and origin-trial.