Refactoring: Make ~CSSStyleSheetResource empty.

Source/core/fetch/CSSStyleSheetResource.cpp

Index: Source/core/fetch/CSSStyleSheetResource.cpp
diff --git a/Source/core/fetch/CSSStyleSheetResource.cpp b/Source/core/fetch/CSSStyleSheetResource.cpp
index 2eab0d54d4a890a7be1cc5089b0d5f850c8c55ba..5d86e05c1784f3e57cad6e5b386e67d938b64d50 100644
--- a/Source/core/fetch/CSSStyleSheetResource.cpp
+++ b/Source/core/fetch/CSSStyleSheetResource.cpp
@@ -49,8 +49,15 @@ CSSStyleSheetResource::CSSStyleSheetResource(const ResourceRequest& resourceRequ
 
 CSSStyleSheetResource::~CSSStyleSheetResource()
 {
+    // Make sure dispose() was cllaed before destruction.
+    ASSERT(!m_parsedStyleSheetCache);
+}
+
+void CSSStyleSheetResource::dispose()
+{
     if (m_parsedStyleSheetCache)
         m_parsedStyleSheetCache->removedFromMemoryCache();
+    m_parsedStyleSheetCache.clear();
 }
 
 void CSSStyleSheetResource::didAddClient(ResourceClient* c)