Rename RootWindowHost to WindowTreeHost

ash/wm/caption_buttons/frame_maximize_button_unittest.cc

Index: ash/wm/caption_buttons/frame_maximize_button_unittest.cc
diff --git a/ash/wm/caption_buttons/frame_maximize_button_unittest.cc b/ash/wm/caption_buttons/frame_maximize_button_unittest.cc
index c0fd2a0a8a9cd57071f41b997e6e765850022da1..57bb9e5cadc770a6f0234ff68caf383117d7cab8 100644
--- a/ash/wm/caption_buttons/frame_maximize_button_unittest.cc
+++ b/ash/wm/caption_buttons/frame_maximize_button_unittest.cc
@@ -558,7 +558,7 @@ TEST_F(FrameMaximizeButtonTest, MaximizeTap) {
                        button_pos,
                        kTouchId,
                        ui::EventTimeForNow());
-  dispatcher->AsRootWindowHostDelegate()->OnHostTouchEvent(&press);
+  dispatcher->AsWindowTreeHostDelegate()->OnHostTouchEvent(&press);
 
   button_pos.Offset(9, 8);
   ui::TouchEvent release(
@@ -566,7 +566,7 @@ TEST_F(FrameMaximizeButtonTest, MaximizeTap) {
       button_pos,
       kTouchId,
       press.time_stamp() + base::TimeDelta::FromMilliseconds(50));
-  dispatcher->AsRootWindowHostDelegate()->OnHostTouchEvent(&release);
+  dispatcher->AsWindowTreeHostDelegate()->OnHostTouchEvent(&release);
 
   ui::GestureConfiguration::set_default_radius(touch_default_radius);
 }