Make gfx::Rect class operations consistently mutate the class they are called on.

ash/wm/system_modal_container_layout_manager.cc

Index: ash/wm/system_modal_container_layout_manager.cc
diff --git a/ash/wm/system_modal_container_layout_manager.cc b/ash/wm/system_modal_container_layout_manager.cc
index 2bfc73ac47fe9a331b799b08b88b69c09c7759c2..22dadc855404bf424814628c6ee16a4a64faa7de 100644
--- a/ash/wm/system_modal_container_layout_manager.cc
+++ b/ash/wm/system_modal_container_layout_manager.cc
@@ -79,7 +79,9 @@ void SystemModalContainerLayoutManager::OnWindowResized() {
   if (!modal_windows_.empty()) {
     aura::Window::Windows::iterator it = modal_windows_.begin();
     for (it = modal_windows_.begin(); it != modal_windows_.end(); ++it) {
-      (*it)->SetBounds((*it)->bounds().AdjustToFit(container_->bounds()));
+      gfx::Rect bounds = (*it)->bounds();
+      bounds.AdjustToFit(container_->bounds());
+      (*it)->SetBounds(bounds);
     }
   }
 }