Move most of the remaining users of WebContentsObserver::tab_contents() to use web_contents().

content/browser/renderer_host/render_view_host_delegate.cc

Index: content/browser/renderer_host/render_view_host_delegate.cc
===================================================================
--- content/browser/renderer_host/render_view_host_delegate.cc	(revision 115777)
+++ content/browser/renderer_host/render_view_host_delegate.cc	(working copy)
@@ -7,6 +7,8 @@
 #include "googleurl/src/gurl.h"
 #include "webkit/glue/webpreferences.h"
 
+using content::WebContents;
+
 RenderViewHostDelegate::View* RenderViewHostDelegate::GetViewDelegate() {
   return NULL;
 }
@@ -28,6 +30,10 @@
   return NULL;
 }
 
+WebContents* RenderViewHostDelegate::GetAsWebContents() {
+  return NULL;
+}
+
 WebPreferences RenderViewHostDelegate::GetWebkitPrefs() {
   return WebPreferences();
 }