Avoid cross-origin iframe issues when loading PDF in print preview

content/public/browser/url_data_source.h

Index: content/public/browser/url_data_source.h
diff --git a/content/public/browser/url_data_source.h b/content/public/browser/url_data_source.h
index c9e5f1c5a041186a36076ce084bf57285f8410bb..4a6e6a40728121c61ae5772ab5890eac2c771ce6 100644
--- a/content/public/browser/url_data_source.h
+++ b/content/public/browser/url_data_source.h
@@ -133,7 +133,7 @@ class CONTENT_EXPORT URLDataSource {
   // information from the URLRequest prior to serving.
   virtual void WillServiceRequest(
       const net::URLRequest* request,
-      std::string* path) const {}
+      std::string* path) const;
 };
 
 }  // namespace content