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

chrome/browser/browsing_data_remover.h

Index: chrome/browser/browsing_data_remover.h
===================================================================
--- chrome/browser/browsing_data_remover.h	(revision 110049)
+++ chrome/browser/browsing_data_remover.h	(working copy)
@@ -6,7 +6,7 @@
 #define CHROME_BROWSER_BROWSING_DATA_REMOVER_H_
 #pragma once
 
-#include <vector>
+#include <set>
 
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
@@ -32,10 +32,6 @@
 class URLRequestContextGetter;
 }
 
-namespace webkit_database {
-class DatabaseTracker;
-}
-
 namespace quota {
 class QuotaManager;
 }