Makes SetFocus() notify callback correctly on failure

components/mus/ws/window_server.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/mus/ws/window_server.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "components/mus/ws/display.h"
 #include "components/mus/ws/display_binding.h"
@@ skipping 219 matching lines @@
 void WindowServer::OnFirstWindowManagerFactorySet() {
   if (display_manager_->has_active_or_pending_displays())
     return;
 
   // We've been supplied a WindowManagerFactory and no displays have been
   // created yet. Treat this as a signal to create a Display.
   // TODO(sky): we need a better way to determine this, most likely a switch.
   delegate_->CreateDefaultDisplays();
 }
 
-void WindowServer::SetFocusedWindow(ServerWindow* window) {
+bool WindowServer::SetFocusedWindow(ServerWindow* window) {
   // TODO(sky): this should fail if there is modal dialog active and |window|
   // is outside that.
   ServerWindow* currently_focused = GetFocusedWindow();
   Display* focused_display =
       currently_focused
           ? display_manager_->GetDisplayContaining(currently_focused)
           : nullptr;
-  if (!window) {
-    if (focused_display)
-      focused_display->SetFocusedWindow(nullptr);
-    return;
-  }
+  if (!window)
+    return focused_display ? focused_display->SetFocusedWindow(nullptr) : true;
+
   Display* display = display_manager_->GetDisplayContaining(window);
   DCHECK(display);  // It's assumed callers do validation before calling this.
-  display->SetFocusedWindow(window);
+  const bool result = display->SetFocusedWindow(window);
   // If the focus actually changed, and focus was in another display, then we
   // need to notify the previously focused display so that it cleans up state
   // and notifies appropriately.
-  if (window && display->GetFocusedWindow() && display != focused_display &&
+  if (result && display->GetFocusedWindow() && display != focused_display &&
       focused_display) {
-    focused_display->SetFocusedWindow(nullptr);
+    const bool cleared_focus = focused_display->SetFocusedWindow(nullptr);
+    DCHECK(cleared_focus);
   }
+  return result;
 }
 
 ServerWindow* WindowServer::GetFocusedWindow() {
   for (Display* display : display_manager_->displays()) {
     ServerWindow* focused_window = display->GetFocusedWindow();
     if (focused_window)
       return focused_window;
   }
   return nullptr;
 }
@@ skipping 362 matching lines @@
 void WindowServer::OnFirstDisplayReady() {
   delegate_->OnFirstDisplayReady();
 }
 
 void WindowServer::OnNoMoreDisplays() {
   delegate_->OnNoMoreDisplays();
 }
 
 }  // namespace ws
 }  // namespace mus