Add a flag to specify whether to show ARC Files app in launcher.

chrome/app/chromeos_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Chrome OS-specific strings (included from generated_resources.grd).
      Everything in this file is wrapped in <if expr="chromeos">. -->
 <grit-part>
   <message name="IDS_EMPTY_STRING" desc="Empty string, exist only to make code generic. No translation required.">
   </message>
   <!-- Idle logout dialog for retail mode -->
   <message name="IDS_IDLE_LOGOUT_TITLE" desc="Dialog title for the idle logout dialog. Used in retail mode only.">
     Are you still there?
   </message>
@@ skipping 70 matching lines @@
   </message>
   <message name="IDS_FLAGS_VIDEO_PLAYER_CHROMECAST_SUPPORT_DESCRIPTION" desc="Description of the about:flag option to the enable the chromecast support for video app.">
     This option enables experimental Chromecast support for Video Player app on ChromeOS.
   </message>
   <message name="IDS_FLAGS_NEW_ZIP_UNPACKER_NAME" desc="Name of about::flags option for the new ZIP unpacker based on the File System Provider API.">
     New ZIP unpacker
   </message>
   <message name="IDS_FLAGS_NEW_ZIP_UNPACKER_DESCRIPTION" desc="Description of about::flags option for the new ZIP unpacker based on the File System Provider API.">
     New ZIP unpacker flow, based on the File System Provider API.
   </message>
+  <message name="IDS_FLAGS_SHOW_ARC_FILES_APP_NAME" desc="Name of about::flags option for showing ARC Files app in launcher.">
+    Show ARC Files app

[Steve McKay, 2017/01/26 19:36:26]

I'm not sure we want to use the word "ARC" in user visible strings (even strings
for nerds fishing around in about:flags). Ping Weifang to see what kind of
terminology to use. Maybe we call it the "Next Generation" file manager. Or
something like that.

+  </message>
+  <message name="IDS_FLAGS_SHOW_ARC_FILES_APP_DESCRIPTION" desc="Description of the about::flag option for showing ARC Files app in launcher.">
+    If enabled, Chrome app launcher will show Files app in ARC container.
+  </message>
   <message name="IDS_FILE_SYSTEM_PROVIDER_UNRESPONSIVE_WARNING" desc="A warning shown in a notification that an operation is taking longer than expected.">
     An operation is taking longer than expected. Do you want to abort it?
   </message>
   <message name="IDS_FILE_SYSTEM_PROVIDER_MANY_UNRESPONSIVE_WARNING" desc="A warning shown in a notification that more than one operations are taking longer than expected.">
     Some operations are taking longer than expected. Do you want to abort them?
   </message>
   <message name="IDS_FILE_SYSTEM_PROVIDER_UNRESPONSIVE_ABORT_BUTTON" desc="Label of the button on the notification about an operation(s) taking to long.">
     Abort
   </message>
   <message name="IDS_FILE_BROWSER_DRIVE_DIRECTORY_LABEL" desc="/drive directory label.">
@@ skipping 6596 matching lines @@
     Attempts left: $1
   </message>
   <message name="IDS_REQUEST_PIN_DIALOG_PIN" desc="The Provider Identification Number abbreviation">
     PIN
   </message>
   <message name="IDS_REQUEST_PIN_DIALOG_PUK" desc="The Personal Unlocking Key (as used in mobile phones) abbreviation">
     PUK
   </message>
 
 </grit-part>