Have media gallery (through native media file util) use MIME sniffer

webkit/fileapi/media/device_media_async_file_util.cc

Index: webkit/fileapi/media/device_media_async_file_util.cc
diff --git a/webkit/fileapi/media/device_media_async_file_util.cc b/webkit/fileapi/media/device_media_async_file_util.cc
index 6235696ded0ad7a8fa692d1d1da720dfc779978b..6740dbdadef909ab58898012de291a9a8a61fd7e 100644
--- a/webkit/fileapi/media/device_media_async_file_util.cc
+++ b/webkit/fileapi/media/device_media_async_file_util.cc
@@ -17,6 +17,7 @@
 #include "webkit/fileapi/media/mtp_device_async_delegate.h"
 #include "webkit/fileapi/media/mtp_device_file_system_config.h"
 #include "webkit/fileapi/media/mtp_device_map_service.h"
+#include "webkit/fileapi/media/native_media_file_util.h"
 
 namespace fileapi {
 
@@ -312,9 +313,11 @@ void DeviceMediaAsyncFileUtil::OnDidCreateSnapshotFile(
     const AsyncFileUtil::CreateSnapshotFileCallback& callback,
     const base::PlatformFileInfo& file_info,
     const base::FilePath& platform_path) {
-  if (!callback.is_null())
-    callback.Run(base::PLATFORM_FILE_OK, file_info, platform_path,
-                 kSnapshotFileTemporary);
+  if (!callback.is_null()) {

[vandebo (ex-Chrome), 2013/03/25 19:02:11]

After looking at this a bit more, I'm not sure it's correct. 
OnSnapshotFileCreatedRunTask is what points to this function and it is passed as
a success callback.  There's something else passed as a failure callback.  So I
think the way the code is structured currently assumes that once we're to this
step there's no way to fail anymore.  With this change that's not the case
anymore.

It would be ok to roll this part back and approach it in a different CL.

[Kevin Bailey, 2013/04/03 18:05:07]

Chatted with vandebo and it looks ok to us, but I will step through it and
figure out who ultimately cares if the create snapshot succeeds or not. There is
a concern that the entity responsible for cleaning up the snapshot file may
think it was never created.

+    base::PlatformFileError error =
+        NativeMediaFileUtil::IsMediaFile(platform_path);
+    callback.Run(error, file_info, platform_path, kSnapshotFileTemporary);
+  }
 }
 
 void DeviceMediaAsyncFileUtil::OnCreateSnapshotFileError(