Oilpan: move DOM string collection objects to the Oilpan heap.

Source/core/dom/ElementRareData.cpp

Index: Source/core/dom/ElementRareData.cpp
diff --git a/Source/core/dom/ElementRareData.cpp b/Source/core/dom/ElementRareData.cpp
index 42d508343a0e7e2fb97e03a468eb3f750b63fcf5..2dd30022a09a913dd4a4b467501310a238f3d367 100644
--- a/Source/core/dom/ElementRareData.cpp
+++ b/Source/core/dom/ElementRareData.cpp
@@ -50,6 +50,11 @@ CSSStyleDeclaration& ElementRareData::ensureInlineCSSStyleDeclaration(Element* o
     return *m_cssomWrapper;
 }
 
+void ElementRareData::trace(Visitor* visitor)
+{
+    visitor->trace(m_dataset);
+    visitor->trace(m_classList);
+}
 
 COMPILE_ASSERT(sizeof(ElementRareData) == sizeof(SameSizeAsElementRareData), ElementRareDataShouldStaySmall);