Uses copy request to flatten the layers to do screen rotation animation.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9e07aab99565dad319f056ae719b88866f574a54..68c18f479870d5f0dd9d96e80361824b14a7b37a 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2416,6 +2416,13 @@ const FeatureEntry kFeatureEntries[] = {
                                     kDelayNavigationFeatureVariations,
                                     "DelayNavigation")},
 
+#if defined(USE_ASH)
+    {"ash-enable-smooth-screen-rotation-animation",
+     IDS_FLAGS_ASH_ENABLE_SMOOTH_SCREEN_ROTATION_ANIMATION_NAME,
+     IDS_FLAGS_ASH_ENABLE_SMOOTH_SCREEN_ROTATION_ANIMATION_DESCRIPTION, kOsCrOS,
+     SINGLE_VALUE_TYPE(ash::switches::kAshEnableSmoothScreenRotationAnimation)},
+#endif  // defined(USE_ASH)
+
     // NOTE: Adding new command-line switches requires adding corresponding
     // entries to enum "LoginCustomFlags" in histograms.xml. See note in
     // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.