Avoid using declarations in headers which introduce symbol conflicts.

third_party/WebKit/Source/modules/webdatabase/InspectorDatabaseAgent.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 36 matching lines @@
     : public InspectorBaseAgent<protocol::Database::Metainfo> {
   WTF_MAKE_NONCOPYABLE(InspectorDatabaseAgent);
 
  public:
   static InspectorDatabaseAgent* create(Page* page) {
     return new InspectorDatabaseAgent(page);
   }
   ~InspectorDatabaseAgent() override;
   DECLARE_VIRTUAL_TRACE();
 
-  Response disable() override;
+  protocol::Response disable() override;
   void restore() override;
   void didCommitLoadForLocalFrame(LocalFrame*) override;
 
   // Called from the front-end.
-  Response enable() override;
-  Response getDatabaseTableNames(
+  protocol::Response enable() override;
+  protocol::Response getDatabaseTableNames(
       const String& databaseId,
       std::unique_ptr<protocol::Array<String>>* names) override;
   void executeSQL(const String& databaseId,
                   const String& query,
                   std::unique_ptr<ExecuteSQLCallback>) override;
 
   void didOpenDatabase(blink::Database*,
                        const String& domain,
                        const String& name,
                        const String& version);
 
  private:
   explicit InspectorDatabaseAgent(Page*);
   void registerDatabaseOnCreation(blink::Database*);
 
   blink::Database* databaseForId(const String& databaseId);
   InspectorDatabaseResource* findByFileName(const String& fileName);
 
   Member<Page> m_page;
   typedef HeapHashMap<String, Member<InspectorDatabaseResource>>
       DatabaseResourcesHeapMap;
   DatabaseResourcesHeapMap m_resources;
   bool m_enabled;
 };
 
 }  // namespace blink
 
 #endif  // !defined(InspectorDatabaseAgent_h)