Rename/tweak some StylePropertySet/CSSStyleDeclaration copying functions.

Source/core/css/CSSComputedStyleDeclaration.cpp

Index: Source/core/css/CSSComputedStyleDeclaration.cpp
diff --git a/Source/core/css/CSSComputedStyleDeclaration.cpp b/Source/core/css/CSSComputedStyleDeclaration.cpp
index 6a2ad4dd6da25d656f67be8e01ce671072f09c4f..1a3080a24ad99eba98cc68765deb367374449d2f 100644
--- a/Source/core/css/CSSComputedStyleDeclaration.cpp
+++ b/Source/core/css/CSSComputedStyleDeclaration.cpp
@@ -2843,7 +2843,7 @@ bool CSSComputedStyleDeclaration::cssPropertyMatches(CSSPropertyID propertyID, c
     return value && propertyValue && value->equals(*propertyValue);
 }
 
-PassRefPtr<StylePropertySet> CSSComputedStyleDeclaration::copy() const
+PassRefPtr<MutableStylePropertySet> CSSComputedStyleDeclaration::copyProperties() const
 {
     return copyPropertiesInSet(computableProperties());
 }
@@ -2896,7 +2896,7 @@ PassRefPtr<CSSValueList> CSSComputedStyleDeclaration::getCSSPropertyValuesForGri
     return list.release();
 }
 
-PassRefPtr<StylePropertySet> CSSComputedStyleDeclaration::copyPropertiesInSet(const Vector<CSSPropertyID>& properties) const
+PassRefPtr<MutableStylePropertySet> CSSComputedStyleDeclaration::copyPropertiesInSet(const Vector<CSSPropertyID>& properties) const
 {
     Vector<CSSProperty, 256> list;
     list.reserveInitialCapacity(properties.size());
@@ -2905,7 +2905,7 @@ PassRefPtr<StylePropertySet> CSSComputedStyleDeclaration::copyPropertiesInSet(co
         if (value)
             list.append(CSSProperty(properties[i], value.release(), false));
     }
-    return StylePropertySet::create(list.data(), list.size());
+    return static_pointer_cast<MutableStylePropertySet>(StylePropertySet::create(list.data(), list.size()));
 }
 
 void CSSComputedStyleDeclaration::reportMemoryUsage(MemoryObjectInfo* memoryObjectInfo) const