Implement a salt for MediaSource IDs that can be cleared by a user.

content/test/test_content_browser_client.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/test/test_content_browser_client.h"
 
 #include <string>
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
@@ skipping 20 matching lines @@
 }
 
 base::FilePath TestContentBrowserClient::GetDefaultDownloadDirectory() {
   if (!download_dir_.IsValid()) {
     bool result = download_dir_.CreateUniqueTempDir();
     CHECK(result);
   }
   return download_dir_.path();
 }
 
+std::string TestContentBrowserClient::GetMediaDeviceIDSalt(
+    ResourceContext* rc) {
+  CHECK(rc);
+  return "test_salt";
+}
+
 }  // namespace content