cros: Add about flag for new overview animations

This cl adds a new flag to turn on/off the new overview animations.

Bug: 801465, 795988
Test: Tested on device can turn on/off the new animations.
Change-Id: I17570006e7d495fad1079e8bf7d9f39a454e24cb
Reviewed-on: https://chromium-review.googlesource.com/924249
Commit-Queue: Tao Wu <[email protected]>
Reviewed-by: Sammie Quon <[email protected]>
Cr-Commit-Position: refs/heads/master@{#537511}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index a67eae3..8af5042 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1846,6 +1846,9 @@
 extern const char kAshEnableNewOverviewUiName[];
 extern const char kAshEnableNewOverviewUiDescription[];
 
+extern const char kAshEnableNewOverviewAnimationsName[];
+extern const char kAshEnableNewOverviewAnimationsDescription[];
+
 extern const char kAshEnablePersistentWindowBoundsName[];
 extern const char kAshEnablePersistentWindowBoundsDescription[];