Allow directories under Linux files mount point as download location

Allow Linux files directories as a downloads location as per
Android files in crosreview.com/1144992.

Bug: 863610
Change-Id: I5ddea45452ffd172231cf5516fc376ed6426e86c
Reviewed-on: https://chromium-review.googlesource.com/1158454Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579947}

chrome/browser/download/download_prefs.cc

@@ -478,6 +478,14 @@ base::FilePath DownloadPrefs::SanitizeDownloadTargetPath(
     return android_files_mount_point.Append(relative);
   }
 
+  // Allow paths under the Linux files mount point.
+  base::FilePath linux_files_mount_point =
+      file_manager::util::GetCrostiniMountDirectory(profile_);
+  if (linux_files_mount_point.AppendRelativePath(path, &relative) &&
+      !relative.ReferencesParent()) {
+    return linux_files_mount_point.Append(relative);
+  }
+
   // Fall back to the default download directory for all other paths.
   return profile_download_dir;
 #endif

chrome/browser/download/download_prefs_unittest.cc

@@ -140,6 +140,13 @@ TEST(DownloadPrefsTest, DownloadDirSanitization) {
   EXPECT_TRUE(prefs.DownloadPath().IsAbsolute());
   EXPECT_EQ(prefs.DownloadPath(), testdir);
 
+  // Test a valid path for Linux files.
+  testdir = base::FilePath("/media/fuse/crostini_test_termina_penguin/testdir");
+  profile.GetPrefs()->SetString(prefs::kDownloadDefaultDirectory,
+                                testdir.value());
+  EXPECT_TRUE(prefs.DownloadPath().IsAbsolute());
+  EXPECT_EQ(prefs.DownloadPath(), testdir);
+
   // Test with an invalid path outside the download directory.
   profile.GetPrefs()->SetString(prefs::kDownloadDefaultDirectory,
                                 "/home/chronos");