chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/api/debugger/debugger_api.h

 // Copyright (c) 2012 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.
 
 // Defines the Chrome Extensions Debugger API functions for attaching debugger
 // to the page.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_DEBUGGER_DEBUGGER_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_DEBUGGER_DEBUGGER_API_H_
 
 #include <string>
 #include <vector>
 
 #include "chrome/browser/extensions/chrome_extension_function.h"
 #include "chrome/common/extensions/api/debugger.h"
 #include "content/public/browser/devtools_agent_host.h"
 
 using extensions::api::debugger::Debuggee;
 
 // Base debugger function.
 
 namespace base {
 class DictionaryValue;
 }
 
-namespace content {
-class WebContents;
-}
-
 namespace extensions {
 class ExtensionDevToolsClientHost;
 
 class DebuggerFunction : public ChromeAsyncExtensionFunction {
  protected:
   DebuggerFunction();
   ~DebuggerFunction() override;
 
   void FormatErrorMessage(const std::string& format);
 
@@ skipping 61 matching lines @@
   // ExtensionFunction:
   bool RunAsync() override;
 
  private:
   void SendTargetList(const content::DevToolsAgentHost::List& target_list);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DEBUGGER_DEBUGGER_API_H_