Rename RootWindowHost* to WindowTreeHost*

ash/wm/workspace/workspace_event_handler_unittest.cc

Index: ash/wm/workspace/workspace_event_handler_unittest.cc
diff --git a/ash/wm/workspace/workspace_event_handler_unittest.cc b/ash/wm/workspace/workspace_event_handler_unittest.cc
index e6e34492e1943bc9976252c4dfbbcceab489986c..1bcaab074333029871c8dfa93d4dd19e66f2e656 100644
--- a/ash/wm/workspace/workspace_event_handler_unittest.cc
+++ b/ash/wm/workspace/workspace_event_handler_unittest.cc
@@ -275,12 +275,12 @@ TEST_F(WorkspaceEventHandlerTest, DoubleClickCaptionTogglesMaximize) {
                        ui::EF_MIDDLE_MOUSE_BUTTON | ui::EF_IS_DOUBLE_CLICK,
                        ui::EF_MIDDLE_MOUSE_BUTTON);
   aura::WindowEventDispatcher* dispatcher = root->GetDispatcher();
-  dispatcher->AsRootWindowHostDelegate()->OnHostMouseEvent(&press);
+  dispatcher->AsWindowTreeHostDelegate()->OnHostMouseEvent(&press);
   ui::MouseEvent release(ui::ET_MOUSE_RELEASED, generator.current_location(),
                          generator.current_location(),
                          ui::EF_IS_DOUBLE_CLICK,
                          ui::EF_MIDDLE_MOUSE_BUTTON);
-  dispatcher->AsRootWindowHostDelegate()->OnHostMouseEvent(&release);
+  dispatcher->AsWindowTreeHostDelegate()->OnHostMouseEvent(&release);
 
   EXPECT_FALSE(window_state->IsMaximized());
   EXPECT_EQ("1,2 30x40", window->bounds().ToString());