Add CefURLRequest::ResponseWasCached method (issue #2283)

include/cef_urlrequest.h

@@ -114,6 +114,13 @@ class CefURLRequest : public virtual CefBaseRefCounted {
   /*--cef()--*/
   virtual CefRefPtr<CefResponse> GetResponse() = 0;
 
+  ///
+  // Returns true if the response body was served from the cache. This includes
+  // responses for which revalidation was required.
+  ///
+  /*--cef()--*/
+  virtual bool ResponseWasCached() = 0;
+
   ///
   // Cancel the request.
   ///