Have Frame::tree() return a reference

Source/core/page/PageGroupLoadDeferrer.cpp

Index: Source/core/page/PageGroupLoadDeferrer.cpp
diff --git a/Source/core/page/PageGroupLoadDeferrer.cpp b/Source/core/page/PageGroupLoadDeferrer.cpp
index d00a5190f75fb9121923e42b40f44adcf617ab85..3f42886a770f8689958c9f70e070d296d4c0a696 100644
--- a/Source/core/page/PageGroupLoadDeferrer.cpp
+++ b/Source/core/page/PageGroupLoadDeferrer.cpp
@@ -49,7 +49,7 @@ PageGroupLoadDeferrer::PageGroupLoadDeferrer(Page* page, bool deferSelf)
 
                 // This code is not logically part of load deferring, but we do not want JS code executed beneath modal
                 // windows or sheets, which is exactly when PageGroupLoadDeferrer is used.
-                for (Frame* frame = otherPage->mainFrame(); frame; frame = frame->tree()->traverseNext())
+                for (Frame* frame = otherPage->mainFrame(); frame; frame = frame->tree().traverseNext())
                     frame->document()->suspendScheduledTasks();
             }
         }
@@ -67,7 +67,7 @@ PageGroupLoadDeferrer::~PageGroupLoadDeferrer()
         if (Page* page = m_deferredFrames[i]->page()) {
             page->setDefersLoading(false);
 
-            for (Frame* frame = page->mainFrame(); frame; frame = frame->tree()->traverseNext())
+            for (Frame* frame = page->mainFrame(); frame; frame = frame->tree().traverseNext())
                 frame->document()->resumeScheduledTasks();
         }
     }