Have Frame::tree() return a reference

Source/core/page/CreateWindow.cpp

Index: Source/core/page/CreateWindow.cpp
diff --git a/Source/core/page/CreateWindow.cpp b/Source/core/page/CreateWindow.cpp
index b740d417dbb196479f8131b27eedddb23ebd089b..10d2694b33295e374e71d6c897839ca0bb2484a7 100644
--- a/Source/core/page/CreateWindow.cpp
+++ b/Source/core/page/CreateWindow.cpp
@@ -66,7 +66,7 @@ static Frame* createWindow(Frame* openerFrame, Frame* lookupFrame, const FrameLo
 
     if (openerFrame->settings() && !openerFrame->settings()->supportsMultipleWindows()) {
         created = false;
-        return openerFrame->tree()->top();
+        return openerFrame->tree().top();
     }
 
     Page* oldPage = openerFrame->page();
@@ -82,7 +82,7 @@ static Frame* createWindow(Frame* openerFrame, Frame* lookupFrame, const FrameLo
     frame->loader()->forceSandboxFlags(openerFrame->document()->sandboxFlags());
 
     if (request.frameName() != "_blank")
-        frame->tree()->setName(request.frameName());
+        frame->tree().setName(request.frameName());
 
     page->chrome().setWindowFeatures(features);