Add command-line flag to force compositor framerate.

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 2a999a81a5094f05a9ba629feafdf8220f444ed4..991aba5e0ef1b54462bd01258d1991601f1d7db1 100644
--- a/ui/compositor/compositor_switches.cc
+++ b/ui/compositor/compositor_switches.cc
@@ -17,6 +17,10 @@ const char kEnableHardwareOverlays[] = "enable-hardware-overlays";
 // Forces tests to produce pixel output when they normally wouldn't.
 const char kEnablePixelOutputInTests[] = "enable-pixel-output-in-tests";
 
+// Limits the compositor to output a certain number of frames per second,
+// maximum.
+const char kLimitFps[] = "limit-fps";
+
 // Disable partial swap which is needed for some OpenGL drivers / emulators.
 const char kUIDisablePartialSwap[] = "ui-disable-partial-swap";