Make chrome/browser/media_galleries compile on Android

chrome/browser/media_galleries/fileapi/mtp_device_map_service.cc

Index: chrome/browser/media_galleries/fileapi/mtp_device_map_service.cc
diff --git a/chrome/browser/media_galleries/fileapi/mtp_device_map_service.cc b/chrome/browser/media_galleries/fileapi/mtp_device_map_service.cc
index 6941878f69c33e8a1711cfa7292fb9c98103a952..92e56b39676aae7b76a1f3f04fc4a09f7072ed80 100644
--- a/chrome/browser/media_galleries/fileapi/mtp_device_map_service.cc
+++ b/chrome/browser/media_galleries/fileapi/mtp_device_map_service.cc
@@ -28,6 +28,11 @@ void MTPDeviceMapService::RegisterMTPFileSystem(
     const base::FilePath::StringType& device_location,
     const std::string& filesystem_id,
     const bool read_only) {
+#if defined(OS_ANDROID)
+  // Skip registering the MTP device as there is no MTPDeviceAsyncDelegate
+  // implementation for Chrome on Android at the moment. (crbug.com/560390)

[no sievers, 2015/11/23 18:43:40]

can we just create a stub that returns null?

[Lei Zhang, 2015/11/23 21:26:51]

Right, is a no-op CreateMTPDeviceAsyncDelegate() sufficient? Or that plus a stub
MTPDeviceAsyncDelegate?

[mohsen, 2015/11/23 21:33:50]

Done, by creating media_galleries/android/ directory containing the stub
implementation. This directory will contain the actual implementation for
MTPDeviceAsyncDelegate in future. How does it look?

+  NOTIMPLEMENTED();
+#else
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
   DCHECK(!device_location.empty());
   DCHECK(!filesystem_id.empty());
@@ -46,6 +51,7 @@ void MTPDeviceMapService::RegisterMTPFileSystem(
 
   mtp_device_usage_map_[key]++;
   mtp_device_map_[filesystem_id] = make_pair(device_location, read_only);
+#endif
 }
 
 void MTPDeviceMapService::RevokeMTPFileSystem(