Adds initial key systems support for Chromecast.

chromecast/media/base/key_systems_common_simple.cc

Index: chromecast/media/base/key_systems_common_simple.cc
diff --git a/chromecast/media/cma/base/decoder_buffer_base.cc b/chromecast/media/base/key_systems_common_simple.cc
similarity index 62%
copy from chromecast/media/cma/base/decoder_buffer_base.cc
copy to chromecast/media/base/key_systems_common_simple.cc
index 40c0a7d006633aca65e72dc2b58e8346e380b394..e6dbd02890298d0f97a9cb64240d6b8f47f75c0a 100644
--- a/chromecast/media/cma/base/decoder_buffer_base.cc
+++ b/chromecast/media/base/key_systems_common_simple.cc
@@ -2,15 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chromecast/media/cma/base/decoder_buffer_base.h"
+#include "chromecast/media/base/key_systems_common.h"
 
 namespace chromecast {
 namespace media {
 
-DecoderBufferBase::DecoderBufferBase() {
-}
-
-DecoderBufferBase::~DecoderBufferBase() {
+CastKeySystem GetPlatformKeySystemByName(const std::string& key_system_name) {
+  return KEY_SYSTEM_NONE;
 }
 
 }  // namespace media