[Media View] Change MyFiles path in Android to use UUID

We have changed the MyFiles path inside Android to use its UUID.
As a result, we need to accordingly change the path constant defined in
RecentArcMediaSource to avoid a duplicate entry in Files app Media View.

BUG=1040386
BUG=1148625
TEST=Edit an image file under MyFiles (by e.g. renaming, rotating).
TEST=Confirm that no duplicate entry for the file is found under the
TEST="Images" and "Recent" tabs in the Chrome OS Files app.

Change-Id: Ib0c72a883b4c959f429af2dea3ad73b29d1563b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2560082Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Youkichi Hosoi <youkichihosoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832704}

chrome/browser/chromeos/fileapi/recent_arc_media_source.cc

@@ -34,7 +34,11 @@ namespace chromeos {
 namespace {
 
 const char kAndroidDownloadDirPrefix[] = "/storage/emulated/0/Download/";
-const char kAndroidMyFilesDirPrefix[] = "/storage/MyFiles/";
+// The path of the MyFiles directory inside Android. The UUID "0000....2019" is
+// defined in components/arc/volume_mounter/arc_volume_mounter_bridge.cc.
+// TODO(crbug.com/929031): Move MyFiles constants to a common place.
+const char kAndroidMyFilesDirPrefix[] =
+    "/storage/0000000000000000000000000000CAFEF00D2019/";
 
 const char kMediaDocumentsProviderAuthority[] =
     "com.android.providers.media.documents";