Refactor StyleVariableData to fallback on root map for performance reasons.

third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.cpp

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2011 Sencha, Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
@@ skipping 11 matching lines @@
  */
 
 #include "core/css/CSSComputedStyleDeclaration.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/CSSPropertyNames.h"
 #include "core/css/CSSPrimitiveValueMappings.h"
 #include "core/css/CSSPropertyMetadata.h"
 #include "core/css/CSSSelector.h"
 #include "core/css/CSSValuePool.h"
+#include "core/css/CSSVariableData.h"
 #include "core/css/ComputedStyleCSSValueMapping.h"
 #include "core/css/parser/CSSParser.h"
 #include "core/css/parser/CSSVariableParser.h"
 #include "core/css/resolver/StyleResolver.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/PseudoElement.h"
 #include "core/layout/LayoutObject.h"
 #include "core/style/ComputedStyle.h"
 #include "wtf/text/StringBuilder.h"
@@ skipping 485 matching lines @@
 }
 
 CSSValue* CSSComputedStyleDeclaration::getPropertyCSSValue(AtomicString customPropertyName) const
 {
     const ComputedStyle* style = computeComputedStyle();
     if (!style)
         return nullptr;
     return ComputedStyleCSSValueMapping::get(customPropertyName, *style);
 }
 
-const HashMap<AtomicString, RefPtr<CSSVariableData>>* CSSComputedStyleDeclaration::getVariables() const
+std::unique_ptr<HashMap<AtomicString, RefPtr<CSSVariableData>>> CSSComputedStyleDeclaration::getVariables() const
 {
     const ComputedStyle* style = computeComputedStyle();
     if (!style)
         return nullptr;
     return ComputedStyleCSSValueMapping::getVariables(*style);
 }
 
 CSSValue* CSSComputedStyleDeclaration::getPropertyCSSValue(CSSPropertyID propertyID) const
 {
     Node* styledNode = this->styledNode();
@@ skipping 155 matching lines @@
     exceptionState.throwDOMException(NoModificationAllowedError, "These styles are computed, and therefore the '" + getPropertyNameString(id) + "' property is read-only.");
 }
 
 DEFINE_TRACE(CSSComputedStyleDeclaration)
 {
     visitor->trace(m_node);
     CSSStyleDeclaration::trace(visitor);
 }
 
 } // namespace blink