cc: Single fullscreen overlay validatator flag.

ui/compositor/compositor_switches.cc

Index: ui/compositor/compositor_switches.cc
diff --git a/ui/compositor/compositor_switches.cc b/ui/compositor/compositor_switches.cc
index c8464ddfdaa140e37c46eb42bb54ff8dfa327825..2139a6049aab66cbc39fa50d31ccd635d502be36 100644
--- a/ui/compositor/compositor_switches.cc
+++ b/ui/compositor/compositor_switches.cc
@@ -10,6 +10,8 @@ namespace switches {
 
 // Enable compositing individual elements via hardware overlays when
 // permitted by device.
+// Setting the flag to "single-fullscreen" will try to promote a single
+// fullscreen overlay and use it as main framebuffer where possible.
 const char kEnableHardwareOverlays[] = "enable-hardware-overlays";
 
 // Forces tests to produce pixel output when they normally wouldn't.