Change the signature of SetScreenshotDelegate() to show ownership transfer more clearly.

ash/accelerators/accelerator_controller.cc

Index: ash/accelerators/accelerator_controller.cc
diff --git a/ash/accelerators/accelerator_controller.cc b/ash/accelerators/accelerator_controller.cc
index 2a48859b43d2f6f3a97d225fbdb80b3bf8040897..8a736d3f740060dce75d8c272c9b93102db0d0e5 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -162,8 +162,8 @@ bool AcceleratorController::Process(const ui::Accelerator& accelerator) {
 }
 
 void AcceleratorController::SetScreenshotDelegate(
-    ScreenshotDelegate* screenshot_delegate) {
-  screenshot_delegate_.reset(screenshot_delegate);
+    scoped_ptr<ScreenshotDelegate> screenshot_delegate) {
+  screenshot_delegate_.swap(screenshot_delegate);
 }
 
 void AcceleratorController::SetCapsLockDelegate(