Move 'mdat' advancement logic to make more sense.

This defers the change from kEmittingSamples to kParsingBoxes until after the
current 'mdat' atom has been cleared in MP4StreamParser.

BUG=
TEST=MP4StreamParserTest


Review URL: https://chromiumcodereview.appspot.com/10821081

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148977 0039d316-1c4b-4281-b951-d872f2087c98

media/mp4/mp4_stream_parser.cc

@@ -80,11 +80,7 @@ bool MP4StreamParser::Parse(const uint8* buf, int size) {
 
   do {
     if (state_ == kParsingBoxes) {
-      if (mdat_tail_ > queue_.head()) {
-        result = queue_.Trim(mdat_tail_);
-      } else {
-        result = ParseBox(&err);
-      }
+      result = ParseBox(&err);
     } else {
       DCHECK_EQ(kEmittingSamples, state_);
       result = EnqueueSample(&audio_buffers, &video_buffers, &err);
@@ -322,6 +318,11 @@ bool MP4StreamParser::EnqueueSample(BufferQueue* audio_buffers,
     if (*err)
       return false;
 
+    // Remain in kEnqueueingSamples state, discarding data, until the end of
+    // the current 'mdat' box has been appended to the queue.
+    if (!queue_.Trim(mdat_tail_))
+      return false;
+
     ChangeState(kParsingBoxes);
     end_of_segment_cb_.Run();
     return true;