blink: Cleanup class/struct forward declarations

third_party/WebKit/Source/core/css/ActiveStyleSheets.h

 // Copyright 2016 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 ActiveStyleSheets_h
 #define ActiveStyleSheets_h
 
 #include "core/CoreExport.h"
 #include "platform/heap/HeapAllocator.h"
 
 namespace blink {
 
 class CSSStyleSheet;
 class RuleSet;
-class StyleEngine;
-class TreeScope;
 
 using ActiveStyleSheet = std::pair<Member<CSSStyleSheet>, Member<RuleSet>>;
 using ActiveStyleSheetVector = HeapVector<ActiveStyleSheet>;
 
 enum ActiveSheetsChange {
   NoActiveSheetsChanged,  // Nothing changed.
   ActiveSheetsChanged,    // Sheets were added and/or inserted.
   ActiveSheetsAppended    // Only additions, and all appended.
 };
 
 CORE_EXPORT ActiveSheetsChange
 compareActiveStyleSheets(const ActiveStyleSheetVector& oldStyleSheets,
                          const ActiveStyleSheetVector& newStyleSheets,
                          HeapVector<Member<RuleSet>>& changedRuleSets);
 
 }  // namespace blink
 
 #endif  // ActiveStyleSheets_h