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

chrome/app/chromeos_strings.grdp

Index: chrome/app/chromeos_strings.grdp
diff --git a/chrome/app/chromeos_strings.grdp b/chrome/app/chromeos_strings.grdp
index 822a2c3037f78fad6d9e790b31be4bef4c127c78..143f7cca1c9176d3970c658984655bd7a96f92e8 100644
--- a/chrome/app/chromeos_strings.grdp
+++ b/chrome/app/chromeos_strings.grdp
@@ -88,6 +88,12 @@ Press any key to continue exploring.
   <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>