Convert USE(NATIVE_FULLSCREEN_VIDEO) to a runtime enabled feature

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 30dc693cb98874fe804fee62dc967e4a508bfcf2..fe11b995a6a00ae1c7a3a20b0caeaa9cb96ba726 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -448,6 +448,9 @@ const char kEnableMonitorProfile[]          = "enable-monitor-profile";
 // Enables use of cache if offline, even if it's stale
 const char kEnableOfflineCacheAccess[]      = "enable-offline-cache-access";
 
+// Enables use of hardware overlay for fullscreen video playback. Android only.
+const char kEnableOverlayFullscreenVideo[]  = "enable-overlay-fullscreen-video";
+
 // Enables overlay scrollbars on Aura or Linux. Does nothing on Mac.
 const char kEnableOverlayScrollbars[]       = "enable-overlay-scrollbars";