Add support for cancellation of demuxer reads.

media/filters/memory_data_source.cc

Index: media/filters/memory_data_source.cc
diff --git a/media/filters/memory_data_source.cc b/media/filters/memory_data_source.cc
index d38803ee702e2d1a017b5f7c3e57d54495f34d7e..7031e42d837e4c413dab32373c6790b00c31a33e 100644
--- a/media/filters/memory_data_source.cc
+++ b/media/filters/memory_data_source.cc
@@ -43,6 +43,8 @@ void MemoryDataSource::Stop() {
   is_stopped_ = true;
 }
 
+void MemoryDataSource::Abort() {}
+
 bool MemoryDataSource::GetSize(int64_t* size_out) {
   *size_out = size_;
   return true;