Allow taking screen shot of a non child window which has delegate to paint.

ash/test/test_screenshot_delegate.cc

 // Copyright 2013 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 "ash/test/test_screenshot_delegate.h"
 
 namespace ash {
 namespace test {
 
 TestScreenshotDelegate::TestScreenshotDelegate()
     : handle_take_screenshot_count_(0),
       handle_take_partial_screenshot_count_(0),
-      handle_take_window_screenshot_count_(0),
-      can_take_screenshot_(true) {
+      can_take_screenshot_(true),
+      selected_window_(nullptr) {
 }
 
 TestScreenshotDelegate::~TestScreenshotDelegate() {
 }
 
 void TestScreenshotDelegate::HandleTakeScreenshotForAllRootWindows() {
   handle_take_screenshot_count_++;
 }
 
 void TestScreenshotDelegate::HandleTakePartialScreenshot(
     aura::Window* window, const gfx::Rect& rect) {
   handle_take_partial_screenshot_count_++;
   last_rect_ = rect;
 }
 
 void TestScreenshotDelegate::HandleTakeWindowScreenshot(aura::Window* window) {
-  handle_take_window_screenshot_count_++;
+  selected_window_ = window;
 }
 
 bool TestScreenshotDelegate::CanTakeScreenshot() {
   return can_take_screenshot_;
 }
 
+const aura::Window* TestScreenshotDelegate::GetSelectedWindowAndReset() {
+  aura::Window* result = selected_window_;
+  selected_window_ = nullptr;
+  return result;
+}
+
 }  // namespace test
 }  // namespace ash