[Picture In Picture] Add about flag for toggle android picture in picture api

Add flag to switch PiP API for android.

Bug: 964374
Change-Id: I71b936ca6b31931983d70f88a37b350dd74dcabd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1644008
Reviewed-by: Kentaro Hara <[email protected]>
Reviewed-by: Becca Hughes <[email protected]>
Commit-Queue: Becca Hughes <[email protected]>
Cr-Commit-Position: refs/heads/master@{#668924}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index f21e223f..adb6bcc 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -81,6 +81,9 @@
 extern const char kEnableMessagesWebPushName[];
 extern const char kEnableMessagesWebPushDescription[];
 
+extern const char kAndroidPictureInPictureAPIName[];
+extern const char kAndroidPictureInPictureAPIDescription[];
+
 extern const char kAndroidSiteSettingsUIRefreshName[];
 extern const char kAndroidSiteSettingsUIRefreshDescription[];