Cleanup: Remove more forward declarations in various chrome/browser directories.

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
===================================================================
--- chrome/browser/io_thread.h	(revision 110049)
+++ chrome/browser/io_thread.h	(working copy)
@@ -18,17 +18,12 @@
 #include "net/base/network_change_notifier.h"
 
 class ChromeNetLog;
-class ChromeURLRequestContextGetter;
 class ExtensionEventRouterForwarder;
 class MediaInternals;
 class PrefProxyConfigTrackerImpl;
 class PrefService;
 class SystemURLRequestContextGetter;
 
-namespace base {
-class ListValue;
-}
-
 namespace net {
 class CertVerifier;
 class CookieStore;