chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/api/declarative_content/content_predicate_evaluator.h

 // Copyright 2015 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_DECLARATIVE_CONTENT_CONTENT_PREDICATE_EVALUATOR_H_
 #define CHROME_BROWSER_EXTENSIONS_API_DECLARATIVE_CONTENT_CONTENT_PREDICATE_EVALUATOR_H_
 
 #include <map>
 #include <vector>
 
 #include "base/macros.h"
 #include "chrome/browser/extensions/api/declarative_content/content_predicate.h"
 
 namespace content {
 class BrowserContext;
 struct FrameNavigateParams;
 struct LoadCommittedDetails;
 class WebContents;
 }  // namespace content
 
 namespace extensions {
 
-class Extension;
-
 // Creates and manages instances of an associated ContentPredicate subclass and
 // tracks the url and browser context state required to evaluate the predicates.
 //
 // A ContentPredicateEvaluator corresponds to a single attribute name across all
 // chrome.declarativeContent.PageStateMatchers provided in all rules in the
 // Declarative Content API. For example, given the rules:
 //
 // var rule1 = {
 //   conditions: [
 //     new chrome.declarativeContent.PageStateMatcher({
@@ skipping 97 matching lines @@
   Delegate();
   virtual ~Delegate();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Delegate);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DECLARATIVE_CONTENT_CONTENT_PREDICATE_EVALUATOR_H_