exo: Clean up cursor code

components/exo/shell_surface.cc

Index: components/exo/shell_surface.cc
diff --git a/components/exo/shell_surface.cc b/components/exo/shell_surface.cc
index 38cb702c942bd42e834801e9018e67a9c94c3fd4..b450804939fb1efd11e85164506b2a34e61f3774 100644
--- a/components/exo/shell_surface.cc
+++ b/components/exo/shell_surface.cc
@@ -1301,41 +1301,40 @@ void ShellSurface::AttemptToStartDrag(int component) {
   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),