ash: Add a feature flag for the Keyboard Shortcut Viewer mojo app

Default is disabled for now. Remove the old commandline switch.

[email protected]

Bug: 841020
Change-Id: Ie5df91612d6c976b0b7f056c7248dc92cee9be68
Reviewed-on: https://chromium-review.googlesource.com/1101505
Commit-Queue: Michael Wasserman <[email protected]>
Reviewed-by: James Cook <[email protected]>
Cr-Commit-Position: refs/heads/master@{#567425}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 2963fa9..b701e177 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1703,6 +1703,9 @@
 extern const char kAshEnableUnifiedDesktopName[];
 extern const char kAshEnableUnifiedDesktopDescription[];
 
+extern const char kAshKeyboardShortcutViewerAppName[];
+extern const char kAshKeyboardShortcutViewerAppDescription[];
+
 extern const char kAshShelfColorName[];
 extern const char kAshShelfColorDescription[];