Implemented screen rotation animation experiment.

ash/ash_switches.cc

Index: ash/ash_switches.cc
diff --git a/ash/ash_switches.cc b/ash/ash_switches.cc
index f11743dd64cd94505fba3a6ea8bae96dc40aa324..fd0ffbc33b8990feac9228931f8af598b2feae69 100644
--- a/ash/ash_switches.cc
+++ b/ash/ash_switches.cc
@@ -61,6 +61,13 @@ const char kAshEnableMirroredScreen[] = "ash-enable-mirrored-screen";
 const char kAshEnablePowerButtonQuickLock[] =
     "ash-enable-power-button-quick-lock";
 
+// Specifies the screen rotation animation to use. Possible values are:
+// "partial-rotation", "partial-rotation-slow", "full-rotation", and
+// "full-rotation-slow". See ash/rotator/screen_rotation_animator.cc for more
+// details.
+const char kAshEnableScreenRotationAnimation[] =
+    "ash-screen-rotation-animation";
+
 // Enables software based mirroring.
 const char kAshEnableSoftwareMirroring[] = "ash-enable-software-mirroring";