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

content/common/child_process.h

Index: content/common/child_process.h
===================================================================
--- content/common/child_process.h	(revision 163290)
+++ content/common/child_process.h	(working copy)
@@ -11,6 +11,7 @@
 #include "base/synchronization/waitable_event.h"
 #include "content/common/content_export.h"
 
+namespace content {
 class ChildThread;
 
 // Base class for child processes of the browser process (i.e. renderer and
@@ -76,4 +77,6 @@
   DISALLOW_COPY_AND_ASSIGN(ChildProcess);
 };
 
+}  // namespace content
+
 #endif  // CONTENT_COMMON_CHILD_PROCESS_H_