Move more files into the content namespace.

content/browser/renderer_host/backing_store.cc

Index: content/browser/renderer_host/backing_store.cc
===================================================================
--- content/browser/renderer_host/backing_store.cc	(revision 147462)
+++ content/browser/renderer_host/backing_store.cc	(working copy)
@@ -4,8 +4,9 @@
 
 #include "content/browser/renderer_host/backing_store.h"
 
-BackingStore::BackingStore(content::RenderWidgetHost* widget,
-                           const gfx::Size& size)
+namespace content {
+
+BackingStore::BackingStore(RenderWidgetHost* widget, const gfx::Size& size)
     : render_widget_host_(widget),
       size_(size) {
 }
@@ -16,3 +17,5 @@
 size_t BackingStore::MemorySize() {
   return size_.GetArea() * 4;
 }
+
+}  // namespace content