Fix MSE GC, make it less aggressive, more spec-compliant

media/renderers/renderer_impl.cc

Index: media/renderers/renderer_impl.cc
diff --git a/media/renderers/renderer_impl.cc b/media/renderers/renderer_impl.cc
index 8efe432a7ccd64f8fb5dc982ff2a17b415fbe05d..8f80973af06839085f56008ead430d1cef3cb458 100644
--- a/media/renderers/renderer_impl.cc
+++ b/media/renderers/renderer_impl.cc
@@ -14,6 +14,7 @@
 #include "base/strings/string_number_conversions.h"
 #include "media/base/audio_renderer.h"
 #include "media/base/bind_to_current_loop.h"
+#include "media/base/buffers.h"
 #include "media/base/demuxer_stream_provider.h"
 #include "media/base/media_switches.h"
 #include "media/base/time_source.h"
@@ -198,6 +199,8 @@ void RendererImpl::SetVolume(float volume) {
 base::TimeDelta RendererImpl::GetMediaTime() {
   // No BelongsToCurrentThread() checking because this can be called from other
   // threads.
+  if (!time_source_)
+    return kNoTimestamp();
   return time_source_->CurrentMediaTime();
 }