Files.app: show the warning message when drive authentication is failed.

When authentication is failed on drive, files.app goes offline-mode. This patch adds message to notify that drive is unreachable and encourage user to log out. 

Major changes: 
- Add the private API to logout (fileBrowserPrivate.logout).
- Add the message "Google Drive could not be reached. Please <log out> and log back in."(IDS_FILE_BROWSER_DRIVE_NOT_REACHED).
- Show this message when |OnRefreshKeyInvalid()| is observed.

BUG=160486
TEST=Clear refresh token on drive-internals, and confirm the offline-mode message shows.

[email protected], [email protected]
[email protected]

Review URL: https://chromiumcodereview.appspot.com/12226034

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@183071 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/extensions/extension_function_histogram_value.h b/chrome/browser/extensions/extension_function_histogram_value.h
index f42e22a2..ce6bae6 100644
--- a/chrome/browser/extensions/extension_function_histogram_value.h
+++ b/chrome/browser/extensions/extension_function_histogram_value.h
@@ -475,6 +475,7 @@
   FILEBROWSERPRIVATE_SEARCHDRIVEMETADATA,
   ECHOPRIVATE_CHECKALLOWREDEEMOFFERS,
   MEDIAGALLERIESPRIVATE_EJECTDEVICE,
+  FILEBROWSERPRIVATE_LOGOUTUSER,
   ENUM_BOUNDARY // Last entry: Add new entries above.
 };