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 724547fde114ae19a1238561db39a0c4f67a88d1..f1b30a4326ff4c2b6244ef3bd204db9833278c7b 100644
--- a/Source/core/fetch/Resource.h
+++ b/Source/core/fetch/Resource.h
@@ -242,6 +242,9 @@ 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) { }
 
@@ -374,6 +377,8 @@ private:
     unsigned m_preloadCount;
     unsigned m_protectorCount;
 
+    String m_cacheIdentifier;
+
     unsigned m_preloadResult : 2; // PreloadResult
     unsigned m_requestedFromNetworkingLayer : 1;