Remove obviously unneeded forward declarations from headers under src/{app,base,net}.

net/proxy/proxy_resolver_v8.h

Index: net/proxy/proxy_resolver_v8.h
diff --git a/net/proxy/proxy_resolver_v8.h b/net/proxy/proxy_resolver_v8.h
index 70a31c27f2b7a1ea3a502510987a665c573fce97..7345f45600820da5853cfb17a90cce7a351d866f 100644
--- a/net/proxy/proxy_resolver_v8.h
+++ b/net/proxy/proxy_resolver_v8.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -9,11 +9,8 @@
 #include "base/scoped_ptr.h"
 #include "net/proxy/proxy_resolver.h"
 
-class MessageLoop;
-
 namespace net {
 
-class HostResolver;
 class ProxyResolverJSBindings;
 
 // Implementation of ProxyResolver that uses V8 to evaluate PAC scripts.