Only run container name detection upon ffmpeg parse failure.

media/base/container_names.h

Index: media/base/container_names.h
diff --git a/media/base/container_names.h b/media/base/container_names.h
index e3885ae4dbe263db54f21229c82786be78fb5deb..f65b3794395dcd44c7c1f48b7a6c4fb02b64f7a7 100644
--- a/media/base/container_names.h
+++ b/media/base/container_names.h
@@ -62,6 +62,9 @@ enum MediaContainerName {
   CONTAINER_MAX               // Must be last
 };
 
+// Minimum size considered for processing.
+enum { kMinimumContainerSize = 12 };
+
 // Determine the container type.
 MEDIA_EXPORT MediaContainerName DetermineContainer(const uint8_t* buffer,
                                                    int buffer_size);