Enable V1app backbutton by default

Added about flag in case for troubleshooting.

BUG=749713
TEST=manual

Change-Id: I2f74535282bb8dccca38a4d8ad6f10af88140c62
Reviewed-on: https://chromium-review.googlesource.com/860522
Commit-Queue: Mitsuru Oshima <[email protected]>
Reviewed-by: Michael Wasserman <[email protected]>
Cr-Commit-Position: refs/heads/master@{#529074}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 6c0d051..36cab2bf 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2457,6 +2457,11 @@
 const char kArcVpnDescription[] =
     "Allow Android VPN clients to tunnel Chrome traffic.";
 
+const char kAshDisableV1AppBackButtonName[] =
+    "Disable BackButton on V1 app window";
+const char kAshDisableV1AppBackButtonDescription[] =
+    "Enable this flag to disable back button on V1 app window.";
+
 const char kAshEnableUnifiedDesktopName[] = "Unified desktop mode";
 const char kAshEnableUnifiedDesktopDescription[] =
     "Enable unified desktop mode which allows a window to span multiple "