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

content/renderer/webplugin_delegate_proxy.h

Index: content/renderer/webplugin_delegate_proxy.h
===================================================================
--- content/renderer/webplugin_delegate_proxy.h	(revision 163290)
+++ content/renderer/webplugin_delegate_proxy.h	(working copy)
@@ -28,7 +28,6 @@
 
 struct NPObject;
 class NPObjectStub;
-class PluginChannelHost;
 struct PluginHostMsg_URLRequest_Params;
 class SkBitmap;
 
@@ -47,6 +46,7 @@
 }
 
 namespace content {
+class PluginChannelHost;
 class RenderViewImpl;
 
 // An implementation of WebPluginDelegate that proxies all calls to