Implement "Key Presence" step in "Encrypted Block Encounted" algorithm in EME.

media/filters/chunk_demuxer_unittest.cc

Index: media/filters/chunk_demuxer_unittest.cc
diff --git a/media/filters/chunk_demuxer_unittest.cc b/media/filters/chunk_demuxer_unittest.cc
index 927636acfc3827081cf6fceb2b607bcf775ffed8..ceb1bb9ac28b80ac791dd60b81931a4475f2d858 100644
--- a/media/filters/chunk_demuxer_unittest.cc
+++ b/media/filters/chunk_demuxer_unittest.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/bind.h"
+#include "base/message_loop.h"
 #include "media/base/audio_decoder_config.h"
 #include "media/base/decoder_buffer.h"
 #include "media/base/mock_callback.h"
@@ -669,6 +670,7 @@ class ChunkDemuxerTest : public testing::Test {
     return true;
   }
 
+  MessageLoop message_loop_;
   MockDemuxerHost host_;
 
   scoped_ptr<MockChunkDemuxerClient> client_;