Load CMA backend from shared library

chromecast/public/media/BUILD.gn

Index: chromecast/public/media/BUILD.gn
diff --git a/chromecast/public/media/BUILD.gn b/chromecast/public/media/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..5b00f0b7cc40df2a28475d01190901af199cdd07
--- /dev/null
+++ b/chromecast/public/media/BUILD.gn
@@ -0,0 +1,19 @@
+# Copyright 2015 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.
+
+source_set("public") {
+  sources = [
+    "audio_pipeline_device.h",
+    "cast_decoder_buffer.h",
+    "cast_decrypt_config.h",
+    "cast_key_system.h",
+    "decoder_config.h",
+    "media_clock_device.h",
+    "media_component_device.h",
+    "media_pipeline_backend.h",
+    "media_pipeline_device_params.h",
+    "stream_id.h",
+    "video_pipeline_device.h",
+  ]
+}