Adds initial key systems support for Chromecast.

chromecast/media/base/key_systems_common_simple.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // 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
 }  // namespace chromecast