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

chrome/browser/flag_descriptions.h

Index: chrome/browser/flag_descriptions.h
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index c11429fd5fe19002ab3842687db5cf1af9cc725a..ed0fac7355b5b23113a20812e86281b98c1f3066 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -786,6 +786,12 @@ extern const char kAshEnableMirroredScreenName[];
 // Description for the flag to enable the mirrored screen mode.
 extern const char kAshEnableMirroredScreenDescription[];
 
+// Title for the flag to enable smooth rotation animations.

[oshima, 2017/03/31 00:14:34]

can you file a bug to cleanup the flag and add reference to it?

[wutao, 2017/04/03 16:16:04]

Created a http://crbug.com/707800 and added it to the main bug.

+extern const char kAshEnableSmoothScreenRotationAnimationName[];
+
+// Description for the flag to enable smooth rotation animations.
+extern const char kAshEnableSmoothScreenRotationAnimationDescription[];
+
 // Description for the flag that sets material design ink drop animation speed
 // of fast.
 extern const char kMaterialDesignInkDropAnimationFast[];