Add flag for enabling horizontal tab switching on Android

This CL adds a flag for making the Android tab switcher always use horizontal
mode (currently used in landscape mode) in portrait mode. Later CLs will refine
the experience so we can run a public experiment.

Bug: 828224
Change-Id: Iee9417c6e6c3b39df07202da453da71da9cbe72b
Reviewed-on: https://chromium-review.googlesource.com/991400
Commit-Queue: Ryan Landay <[email protected]>
Reviewed-by: Matthew Jones <[email protected]>
Cr-Commit-Position: refs/heads/master@{#547933}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index c5b65ea..2fe3c70 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -501,6 +501,9 @@
 extern const char kHarfbuzzRendertextName[];
 extern const char kHarfbuzzRendertextDescription[];
 
+extern const char kHorizontalTabSwitcherAndroidName[];
+extern const char kHorizontalTabSwitcherAndroidDescription[];
+
 extern const char kViewsCastDialogName[];
 extern const char kViewsCastDialogDescription[];