Include <algorithm> if you use functions from <algorithm>.

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

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2008, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 13 matching lines @@
 #include "core/CSSPropertyNames.h"
 #include "core/CoreExport.h"
 #include "core/css/CSSPrimitiveValue.h"
 #include "core/css/CSSProperty.h"
 #include "core/css/PropertySetCSSStyleDeclaration.h"
 #include "core/css/parser/CSSParserMode.h"
 #include "wtf/ListHashSet.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/Vector.h"
 #include "wtf/text/WTFString.h"
+#include <algorithm>
 
 namespace blink {
 
 class CSSStyleDeclaration;
 class ImmutableStylePropertySet;
 class MutableStylePropertySet;
 class StyleSheetContents;
 
 class CORE_EXPORT StylePropertySet : public RefCountedWillBeGarbageCollectedFinalized<StylePropertySet> {
     WTF_MAKE_NONCOPYABLE(StylePropertySet);
@@ skipping 268 matching lines @@
 inline int StylePropertySet::findPropertyIndex(T property) const
 {
     if (m_isMutable)
         return toMutableStylePropertySet(this)->findPropertyIndex(property);
     return toImmutableStylePropertySet(this)->findPropertyIndex(property);
 }
 
 } // namespace blink
 
 #endif // StylePropertySet_h