Have Frame::tree() return a reference

Source/core/page/EventHandler.cpp

Index: Source/core/page/EventHandler.cpp
diff --git a/Source/core/page/EventHandler.cpp b/Source/core/page/EventHandler.cpp
index 5b875ba1219d25c240b878511b4b65adb65f296d..0d696bf5228e63e9998ee608b42d44df0a976251 100644
--- a/Source/core/page/EventHandler.cpp
+++ b/Source/core/page/EventHandler.cpp
@@ -974,7 +974,7 @@ bool EventHandler::scrollRecursively(ScrollDirection direction, ScrollGranularit
     FrameView* view = frame->view();
     if (view && view->scroll(direction, granularity))
         return true;
-    frame = frame->tree()->parent();
+    frame = frame->tree().parent();
     if (!frame)
         return false;
     return frame->eventHandler()->scrollRecursively(direction, granularity, m_frame->ownerElement());
@@ -997,7 +997,7 @@ bool EventHandler::logicalScrollRecursively(ScrollLogicalDirection direction, Sc
     if (scrolled)
         return true;
 
-    frame = frame->tree()->parent();
+    frame = frame->tree().parent();
     if (!frame)
         return false;
 
@@ -1307,7 +1307,7 @@ bool EventHandler::handleMousePressEvent(const PlatformMouseEvent& mouseEvent)
         return true;
 
     UserGestureIndicator gestureIndicator(DefinitelyProcessingUserGesture);
-    m_frame->tree()->top()->eventHandler()->m_lastMouseDownUserGestureToken = gestureIndicator.currentToken();
+    m_frame->tree().top()->eventHandler()->m_lastMouseDownUserGestureToken = gestureIndicator.currentToken();
 
     cancelFakeMouseMoveEvent();
     if (m_eventHandlerWillResetCapturingMouseEventsNode)
@@ -1568,7 +1568,7 @@ bool EventHandler::handleMouseMoveOrLeaveEvent(const PlatformMouseEvent& mouseEv
     RefPtr<Frame> newSubframe = m_capturingMouseEventsNode.get() ? subframeForTargetNode(m_capturingMouseEventsNode.get()) : subframeForHitTestResult(mev);
 
     // We want mouseouts to happen first, from the inside out.  First send a move event to the last subframe so that it will fire mouseouts.
-    if (m_lastMouseMoveEventSubframe && m_lastMouseMoveEventSubframe->tree()->isDescendantOf(m_frame) && m_lastMouseMoveEventSubframe != newSubframe)
+    if (m_lastMouseMoveEventSubframe && m_lastMouseMoveEventSubframe->tree().isDescendantOf(m_frame) && m_lastMouseMoveEventSubframe != newSubframe)
         passMouseMoveEventToSubframe(mev, m_lastMouseMoveEventSubframe.get());
 
     if (newSubframe) {
@@ -1645,8 +1645,8 @@ bool EventHandler::handleMouseReleaseEvent(const PlatformMouseEvent& mouseEvent)
 
     OwnPtr<UserGestureIndicator> gestureIndicator;
 
-    if (m_frame->tree()->top()->eventHandler()->m_lastMouseDownUserGestureToken)
-        gestureIndicator = adoptPtr(new UserGestureIndicator(m_frame->tree()->top()->eventHandler()->m_lastMouseDownUserGestureToken.release()));
+    if (m_frame->tree().top()->eventHandler()->m_lastMouseDownUserGestureToken)
+        gestureIndicator = adoptPtr(new UserGestureIndicator(m_frame->tree().top()->eventHandler()->m_lastMouseDownUserGestureToken.release()));
     else
         gestureIndicator = adoptPtr(new UserGestureIndicator(DefinitelyProcessingUserGesture));