Reduce header dependencies in net/

net/base/filter.h

Index: net/base/filter.h
diff --git a/net/base/filter.h b/net/base/filter.h
index 295d80f7ebc9384b34b1e220474f3e1085494f5a..cb28031699dda1c9a3f849243e1e3deca6538f3d 100644
--- a/net/base/filter.h
+++ b/net/base/filter.h
@@ -33,12 +33,17 @@
 #include <vector>
 
 #include "base/basictypes.h"
+#include "base/ref_counted.h"
 #include "base/scoped_ptr.h"
 #include "base/time.h"
-#include "net/base/io_buffer.h"
-#include "googleurl/src/gurl.h"
 #include "testing/gtest/include/gtest/gtest_prod.h"
 
+class GURL;
+
+namespace net {
+class IOBuffer;
+}
+
 //------------------------------------------------------------------------------
 // Define an interface class that allows access to contextual information
 // supplied by the owner of this filter.  In the case where there are a chain of