Add UMA stats for audio/video containers.

media/filters/ffmpeg_glue.cc

Index: media/filters/ffmpeg_glue.cc
diff --git a/media/filters/ffmpeg_glue.cc b/media/filters/ffmpeg_glue.cc
index e3b227b2ac5140f74f9057090d0bafdb26429961..a65a914f1eb3b14ed2d092a3080e149119ca0122 100644
--- a/media/filters/ffmpeg_glue.cc
+++ b/media/filters/ffmpeg_glue.cc
@@ -7,6 +7,7 @@
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/synchronization/lock.h"
+#include "media/base/container_names.h"
 #include "media/ffmpeg/ffmpeg_common.h"
 
 namespace media {
@@ -123,7 +124,8 @@ void FFmpegGlue::InitializeFFmpeg() {
 }
 
 FFmpegGlue::FFmpegGlue(FFmpegURLProtocol* protocol)
-    : open_called_(false) {
+    : open_called_(false),
+      protocol_(protocol) {
   InitializeFFmpeg();
 
   // Initialize an AVIOContext using our custom read and seek operations.  Don't
@@ -157,7 +159,26 @@ bool FFmpegGlue::OpenContext() {
 
   // By passing NULL for the filename (second parameter) we are telling FFmpeg
   // to use the AVIO context we setup from the AVFormatContext structure.
-  return avformat_open_input(&format_context_, NULL, NULL, NULL) == 0;
+  int result = avformat_open_input(&format_context_, NULL, NULL, NULL);
+  if (result == 0) {
+    // FFmpeg decoded the container, so report what it found
+    container_names::LogContainer(format_context_->iformat->name);
+    return true;
+  }
+
+  // Stream was not recognized by FFmpeg. Re-read part of the stream and see if
+  // the stream can be recognized. Unfortunately FFmpeg has released the buffer
+  // where it read the header, so we need to read it again. We leave the stream
+  // position unchanged.

[scherkus (not reviewing), 2013/05/07 00:50:20]

As mentioned in container_names.cc, let's focus on our own container guessing
code and not rely on AVFormatContext.

In that case, we should alter this code to run prior to avformat_open_input().

[jrummell, 2013/05/16 23:48:01]

Done.

+  int64 pos;
+  scoped_ptr<uint8[]> buffer(new uint8[8192]);
+
+  protocol_->GetPosition(&pos);
+  protocol_->SetPosition(0);
+  int numRead = protocol_->Read(8192, buffer.get());

[scherkus (not reviewing), 2013/05/07 00:50:20]

it's possible for this to return an error if (for example) the network
connection terminates before returning 8192 bytes

[jrummell, 2013/05/16 23:48:01]

Done.

+  protocol_->SetPosition(pos);
+  container_names::LogContainer(buffer.get(), numRead);
+  return false;
 }
 
 FFmpegGlue::~FFmpegGlue() {