Allow file:/// access to the directory of Android files.

The root directory for Android files (the user's "emulated
external storage", which is accessible from Android file picker)
is mounted on a fixed path on Chrome OS side:
/run/arc/sdcard/write/emulated/0.
We need to whitelist the path so that Chrome can open
Android files using file:// protocol.

Bug: 863515
Test: Manually tested on ARC-enabled Kevin device.
Change-Id: Ic48e46b5a55d75630c6e6b06467ab4597345e6e7
Reviewed-on: https://chromium-review.googlesource.com/1170151
Commit-Queue: Naoki Fukino <fukino@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582851}

chrome/browser/net/chrome_network_delegate.cc

@@ -92,6 +92,7 @@ bool IsAccessAllowedInternal(const base::FilePath& path,
       "/home/chronos/user/WebRTC Logs",
       "/media",
       "/opt/oem",
+      "/run/arc/sdcard/write/emulated/0",
       "/usr/share/chromeos-assets",
       "/var/log",
   };