Change media galleries to external file system type to add toURL support

chrome/browser/media_galleries/fileapi/media_file_system_backend.h

Index: chrome/browser/media_galleries/fileapi/media_file_system_backend.h
diff --git a/chrome/browser/media_galleries/fileapi/media_file_system_backend.h b/chrome/browser/media_galleries/fileapi/media_file_system_backend.h
index 7dbfbd139faffe4bd12c12ff47b78b4af240cacb..a07bc987b7ab9d8c9d57b3396a7b35f21f09e2ab 100644
--- a/chrome/browser/media_galleries/fileapi/media_file_system_backend.h
+++ b/chrome/browser/media_galleries/fileapi/media_file_system_backend.h
@@ -5,20 +5,29 @@
 #ifndef CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_MEDIA_FILE_SYSTEM_BACKEND_H_
 #define CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_MEDIA_FILE_SYSTEM_BACKEND_H_
 
+#include <string>
+
+#include "base/callback.h"
+#include "base/files/file.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "chrome/browser/media_galleries/media_galleries_preferences.h"
 #include "webkit/browser/fileapi/file_system_backend.h"
 
 namespace base {
 class SequencedTaskRunner;
 }
 
+namespace fileapi {
+class FileSystemURL;
+}
+
 namespace net {
 class URLRequest;
 }
 
 class MediaPathFilter;
-
+class Profile;
 class DeviceMediaAsyncFileUtil;
 
 class MediaFileSystemBackend : public fileapi::FileSystemBackend {
@@ -33,6 +42,10 @@ class MediaFileSystemBackend : public fileapi::FileSystemBackend {
   static bool CurrentlyOnMediaTaskRunnerThread();
   static scoped_refptr<base::SequencedTaskRunner> MediaTaskRunner();
 
+  static std::string ConstructMountName(Profile* profile,
+                                        const std::string& extension_id,
+                                        MediaGalleryPrefId pref_id);
+
   static bool AttemptAutoMountForURLRequest(
       const net::URLRequest* url_request,
       const fileapi::FileSystemURL& filesystem_url,