Move a bunch of code in content\common (as well as a few left in renderer) to the content namespace.

content/common/gpu/client/gpu_video_decode_accelerator_host.h

Index: content/common/gpu/client/gpu_video_decode_accelerator_host.h
===================================================================
--- content/common/gpu/client/gpu_video_decode_accelerator_host.h	(revision 163290)
+++ content/common/gpu/client/gpu_video_decode_accelerator_host.h	(working copy)
@@ -12,6 +12,7 @@
 #include "ipc/ipc_listener.h"
 #include "media/video/video_decode_accelerator.h"
 
+namespace content {
 class GpuChannelHost;
 
 // This class is used to talk to VideoDecodeAccelerator in the Gpu process
@@ -71,4 +72,6 @@
   DISALLOW_COPY_AND_ASSIGN(GpuVideoDecodeAcceleratorHost);
 };
 
+}  // namespace content
+
 #endif  // CONTENT_COMMON_GPU_CLIENT_GPU_VIDEO_DECODE_ACCELERATOR_HOST_H_