Log MediaSource parsing errors to the MediaLog so they can appear in chrome:media-internals.

media/base/media_log.h

Index: media/base/media_log.h
diff --git a/media/base/media_log.h b/media/base/media_log.h
index 3ad2c0b7b1cbc42c2ec73ad6be8b00e3a1a810af..e776ef6a8b80026adf09425c038ff412a271ff51 100644
--- a/media/base/media_log.h
+++ b/media/base/media_log.h
@@ -5,6 +5,9 @@
 #ifndef MEDIA_BASE_MEDIA_LOG_H_
 #define MEDIA_BASE_MEDIA_LOG_H_
 
+#include <sstream>
+#include <string>
+
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "media/base/media_export.h"
@@ -14,6 +17,25 @@
 
 namespace media {
 
+// Indicates a string should be added to the log.
+// First parameter - The string to add to the log.
+typedef base::Callback<void(const std::string&)> LogCB;
+
+// Helper class to make it easier to use log_cb like DVLOG().
+class LogHelper {
+ public:
+  LogHelper(const LogCB& Log_cb);
+  ~LogHelper();
+
+  std::ostream& stream() { return stream_; }
+
+ private:
+  LogCB log_cb_;
+  std::stringstream stream_;
+};
+
+#define MEDIA_LOG(log_cb) LogHelper(log_cb).stream()
+
 class MEDIA_EXPORT MediaLog : public base::RefCountedThreadSafe<MediaLog> {
  public:
   // Convert various enums to strings.
@@ -43,6 +65,8 @@ class MEDIA_EXPORT MediaLog : public base::RefCountedThreadSafe<MediaLog> {
       size_t width, size_t height);
   scoped_ptr<MediaLogEvent> CreateBufferedExtentsChangedEvent(
       size_t start, size_t current, size_t end);
+  scoped_ptr<MediaLogEvent> CreateMediaSourceErrorEvent(
+      const std::string& error);
 
  protected:
   friend class base::RefCountedThreadSafe<MediaLog>;