MemoryCache: Enable MemoryCache to have multiple isolated resource maps

Source/core/fetch/Resource.h

Index: Source/core/fetch/Resource.h
diff --git a/Source/core/fetch/Resource.h b/Source/core/fetch/Resource.h
index 2a6926281bd2cf346439d90a91da0b0c2da15378..af0525d91bd8b6d030efbe7f5c54430728246eac 100644
--- a/Source/core/fetch/Resource.h
+++ b/Source/core/fetch/Resource.h
@@ -243,6 +243,9 @@ public:
     bool wasPurged() const;
     bool lock();
 
+    void setCacheIdentifier(const String& cacheIdentifier) { m_cacheIdentifier = cacheIdentifier; }
+    String cacheIdentifier() const { return m_cacheIdentifier; };
+
     virtual void didSendData(unsigned long long /* bytesSent */, unsigned long long /* totalBytesToBeSent */) { }
     virtual void didDownloadData(int) { }
 
@@ -375,6 +378,8 @@ private:
     unsigned m_preloadCount;
     unsigned m_protectorCount;
 
+    String m_cacheIdentifier;
+
     unsigned m_preloadResult : 2; // PreloadResult
     unsigned m_requestedFromNetworkingLayer : 1;