Split out const/non-const variants of Resource::resourceRequest().

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 635bcc5ab67d6f57ccb5a75114184cd8d3a9a0ab..5339ef812eecad261e5d7298084b325a85187c8b 100644
--- a/Source/core/fetch/Resource.h
+++ b/Source/core/fetch/Resource.h
@@ -111,8 +111,10 @@ public:
 
     virtual bool shouldIgnoreHTTPStatusCodeErrors() const { return false; }
 
-    ResourceRequest& resourceRequest() { return m_resourceRequest; }
-    const ResourceRequest& lastResourceRequest();
+    ResourceRequest& mutableResourceRequest() { return m_resourceRequest; }
+    const ResourceRequest& resourceRequest() const { return m_resourceRequest; }
+    const ResourceRequest& lastResourceRequest() const;
+
     const KURL& url() const { return m_resourceRequest.url();}
     Type type() const { return static_cast<Type>(m_type); }
     const ResourceLoaderOptions& options() const { return m_options; }