Have Frame::loader() return a reference

Source/core/testing/MockPagePopupDriver.cpp

Index: Source/core/testing/MockPagePopupDriver.cpp
diff --git a/Source/core/testing/MockPagePopupDriver.cpp b/Source/core/testing/MockPagePopupDriver.cpp
index 48fceda8052cddb6e31ffc583977df9e3d7ae1fc..4902ca001966699e1eace64dd276d2de71b37208 100644
--- a/Source/core/testing/MockPagePopupDriver.cpp
+++ b/Source/core/testing/MockPagePopupDriver.cpp
@@ -71,11 +71,11 @@ inline MockPagePopup::MockPagePopup(PagePopupClient* client, const IntRect& orig
     if (document->body())
         document->body()->appendChild(m_iframe.get());
     Frame* contentFrame = m_iframe->contentFrame();
-    DocumentWriter* writer = contentFrame->loader()->activeDocumentLoader()->beginWriting("text/html", "UTF-8");
+    DocumentWriter* writer = contentFrame->loader().activeDocumentLoader()->beginWriting("text/html", "UTF-8");
     const char scriptToSetUpPagePopupController[] = "<script>window.pagePopupController = parent.internals.pagePopupController;</script>";
     writer->addData(scriptToSetUpPagePopupController, sizeof(scriptToSetUpPagePopupController));
     m_popupClient->writeDocument(*writer);
-    contentFrame->loader()->activeDocumentLoader()->endWriting(writer);
+    contentFrame->loader().activeDocumentLoader()->endWriting(writer);
 }
 
 PassRefPtr<MockPagePopup> MockPagePopup::create(PagePopupClient* client, const IntRect& originBoundsInRootView, Frame* mainFrame)