MSE: Log to chrome://media-internals the buffering API being used

Logs either "ChunkDemuxer: buffering by PTS" or ... "by DTS" to
chrome://media-internals on MSE demuxer construction. This assists in
manual verification and debugging.

Tested with/without --enable-features=MseBufferByPts in cmdline

BUG=718641

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I418fb8e9d89bbfc98c343b2db6effc8a03201794
Reviewed-on: https://chromium-review.googlesource.com/689865
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505245}

media/base/test_helpers.h

@@ -353,6 +353,11 @@ MATCHER_P2(NoSpliceForBadMux, overlapped_buffer_count, splice_time_us, "") {
                                   base::IntToString(splice_time_us));
 }
 
+MATCHER_P(BufferingByPtsDts, by_pts_bool, "") {
+  return CONTAINS_STRING(arg, std::string("ChunkDemuxer: buffering by ") +
+                                  (by_pts_bool ? "PTS" : "DTS"));
+}
+
 }  // namespace media
 
 #endif  // MEDIA_BASE_TEST_HELPERS_H_

media/filters/chunk_demuxer.cc

@@ -468,6 +468,9 @@ ChunkDemuxer::ChunkDemuxer(
       buffering_by_pts_(base::FeatureList::IsEnabled(kMseBufferByPts)) {
   DCHECK(!open_cb_.is_null());
   DCHECK(!encrypted_media_init_data_cb_.is_null());
+  MEDIA_LOG(INFO, media_log_)
+      << GetDisplayName()
+      << (buffering_by_pts_ ? ": buffering by PTS" : ": buffering by DTS");
 }
 
 std::string ChunkDemuxer::GetDisplayName() const {

media/filters/chunk_demuxer_unittest.cc

@@ -215,6 +215,8 @@ class ChunkDemuxerTest : public ::testing::TestWithParam<BufferingApi> {
         base::Bind(&ChunkDemuxerTest::OnProgress, base::Unretained(this));
     Demuxer::EncryptedMediaInitDataCB encrypted_media_init_data_cb = base::Bind(
         &ChunkDemuxerTest::OnEncryptedMediaInitData, base::Unretained(this));
+    EXPECT_MEDIA_LOG(
+        BufferingByPtsDts(buffering_api_ == BufferingApi::kNewByPts));
     demuxer_.reset(new ChunkDemuxer(open_cb, progress_cb,
                                     encrypted_media_init_data_cb, &media_log_));
   }