exo: Clean up cursor code

components/exo/shell_surface.cc

 // Copyright 2015 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/exo/shell_surface.h"
 
 #include <algorithm>
 
 #include "ash/common/frame/custom_frame_view_ash.h"
 #include "ash/common/shelf/wm_shelf.h"
@@ skipping 1283 matching lines @@
   if (resizer_)
     return;
 
   aura::Window* window = GetDragWindow();
   if (!window || window->HasCapture())
     return;
 
   if (bounds_mode_ == BoundsMode::SHELL) {
     // Set the cursor before calling CreateWindowResizer(), as that will
     // eventually call LockCursor() and prevent the cursor from changing.
-    aura::client::CursorClient* cursor_client =
-        aura::client::GetCursorClient(window->GetRootWindow());
-    DCHECK(cursor_client);
-
-    switch (component) {
-      case HTCAPTION:
-        cursor_client->SetCursor(ui::kCursorPointer);
-        break;
-      case HTTOP:
-        cursor_client->SetCursor(ui::kCursorNorthResize);
-        break;
-      case HTTOPRIGHT:
-        cursor_client->SetCursor(ui::kCursorNorthEastResize);
-        break;
-      case HTRIGHT:
-        cursor_client->SetCursor(ui::kCursorEastResize);
-        break;
-      case HTBOTTOMRIGHT:
-        cursor_client->SetCursor(ui::kCursorSouthEastResize);
-        break;
-      case HTBOTTOM:
-        cursor_client->SetCursor(ui::kCursorSouthResize);
-        break;
-      case HTBOTTOMLEFT:
-        cursor_client->SetCursor(ui::kCursorSouthWestResize);
-        break;
-      case HTLEFT:
-        cursor_client->SetCursor(ui::kCursorWestResize);
-        break;
-      case HTTOPLEFT:
-        cursor_client->SetCursor(ui::kCursorNorthWestResize);
-        break;
-      default:
-        NOTREACHED();
-        break;
+    if (auto* cursor_client =

[reveman, 2017/03/28 07:25:15]

nit: this is a change in behavior (we asserted the cursor client is set before)
and I'm not a fan of assignment inside conditionals. please restore structure as
before and if the change in behavior is needed then explain why 

[Dominik Laskowski, 2017/03/30 01:01:18]

Restored. The DCHECK is technically correct, since in theory GetCursorClient
should never return null for root windows. However, it currently returns null in
Mus. Also, this is the only caller that makes the non-null assumption, which is
confusing.

On second thought, the drag should not be started in this case, so I've replaced
the DCHECK with an early return.

+            aura::client::GetCursorClient(window->GetRootWindow())) {
+      switch (component) {
+        case HTCAPTION:
+          cursor_client->SetCursor(ui::kCursorPointer);
+          break;
+        case HTTOP:
+          cursor_client->SetCursor(ui::kCursorNorthResize);
+          break;
+        case HTTOPRIGHT:
+          cursor_client->SetCursor(ui::kCursorNorthEastResize);
+          break;
+        case HTRIGHT:
+          cursor_client->SetCursor(ui::kCursorEastResize);
+          break;
+        case HTBOTTOMRIGHT:
+          cursor_client->SetCursor(ui::kCursorSouthEastResize);
+          break;
+        case HTBOTTOM:
+          cursor_client->SetCursor(ui::kCursorSouthResize);
+          break;
+        case HTBOTTOMLEFT:
+          cursor_client->SetCursor(ui::kCursorSouthWestResize);
+          break;
+        case HTLEFT:
+          cursor_client->SetCursor(ui::kCursorWestResize);
+          break;
+        case HTTOPLEFT:
+          cursor_client->SetCursor(ui::kCursorNorthWestResize);
+          break;
+        default:
+          NOTREACHED();
+          break;
+      }
     }
 
     resizer_ = ash::CreateWindowResizer(ash::WmWindow::Get(window),
                                         GetMouseLocation(), component,
                                         aura::client::WINDOW_MOVE_SOURCE_MOUSE);
     if (!resizer_)
       return;
 
     // Apply pending origin offsets and resize direction before starting a
     // new resize operation. These can still be pending if the client has
@@ skipping 349 matching lines @@
 gfx::Point ShellSurface::GetMouseLocation() const {
   aura::Window* const root_window = widget_->GetNativeWindow()->GetRootWindow();
   gfx::Point location =
       root_window->GetHost()->dispatcher()->GetLastMouseLocationInRoot();
   aura::Window::ConvertPointToTarget(
       root_window, widget_->GetNativeWindow()->parent(), &location);
   return location;
 }
 
 }  // namespace exo