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

chrome/browser/chrome_content_browser_client.cc

Index: chrome/browser/chrome_content_browser_client.cc
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index 33a142bbd72207b68f0150ec55b3fbac30911912..664cdfe776acc63017a20bc3db14b14c3a3699fe 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -48,6 +48,7 @@
 #include "chrome/browser/local_discovery/storage/privet_filesystem_backend.h"
 #include "chrome/browser/media/cast_transport_host_filter.h"
 #include "chrome/browser/media/media_capture_devices_dispatcher.h"
+#include "chrome/browser/media_galleries/fileapi/media_file_system_backend.h"
 #include "chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.h"
 #include "chrome/browser/nacl_host/nacl_browser_delegate_impl.h"
 #include "chrome/browser/net/chrome_net_log.h"
@@ -2552,6 +2553,10 @@ void ChromeContentBrowserClient::GetAdditionalAllowedSchemesForFileSystem(
 
 void ChromeContentBrowserClient::GetURLRequestAutoMountHandlers(
     std::vector<fileapi::URLRequestAutoMountHandler>* handlers) {
+#if !defined(OS_ANDROID)
+  handlers->push_back(
+      base::Bind(MediaFileSystemBackend::AttemptAutoMountForURLRequest));
+#endif  // OS_ANDROID
 }
 
 void ChromeContentBrowserClient::GetAdditionalFileSystemBackends(