Only run container name detection upon ffmpeg parse failure.

media/base/container_names.cc

Index: media/base/container_names.cc
diff --git a/media/base/container_names.cc b/media/base/container_names.cc
index 34875b51f0f2b4b9859b8e561e5416da179728ab..afa71cad34eee53046b60d482b2b5242ccfdc26e 100644
--- a/media/base/container_names.cc
+++ b/media/base/container_names.cc
@@ -1425,7 +1425,7 @@ static const uint8_t kWtvSignature[] = {0xb7, 0xd8, 0x00, 0x20, 0x37, 0x49,
 static MediaContainerName LookupContainerByFirst4(const uint8_t* buffer,
                                                   int buffer_size) {
   // Minimum size that the code expects to exist without checking size.
-  if (buffer_size < 12)
+  if (buffer_size < kMinimumContainerSize)
     return CONTAINER_UNKNOWN;
 
   uint32_t first4 = Read32(buffer);