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

content/renderer/pepper/pepper_platform_context_3d_impl.h

Index: content/renderer/pepper/pepper_platform_context_3d_impl.h
===================================================================
--- content/renderer/pepper/pepper_platform_context_3d_impl.h	(revision 163290)
+++ content/renderer/pepper/pepper_platform_context_3d_impl.h	(working copy)
@@ -14,18 +14,14 @@
 
 #ifdef ENABLE_GPU
 
+class CommandBufferProxy;
 namespace gpu {
-
 class CommandBuffer;
-
 }  // namespace gpu
 
-class CommandBufferProxy;
+namespace content {
 class GpuChannelHost;
-class ContentGLContext;
 
-namespace content {
-
 class PepperParentContextProvider;
 
 class PlatformContext3DImpl