Fix Volume slider is captured in screenshot done in touchview mode

ash/wm/lock_state_controller_unittest.cc

Index: ash/wm/lock_state_controller_unittest.cc
diff --git a/ash/wm/lock_state_controller_unittest.cc b/ash/wm/lock_state_controller_unittest.cc
index 2ab2532bd4e918b211997af34a3f2a2043c907d3..d23035f47c1404b278bb4d687124f2cca82e6f09 100644
--- a/ash/wm/lock_state_controller_unittest.cc
+++ b/ash/wm/lock_state_controller_unittest.cc
@@ -19,6 +19,9 @@
 #include "ash/wm/power_button_controller.h"
 #include "ash/wm/session_state_animator.h"
 #include "base/memory/scoped_vector.h"
+#include "base/run_loop.h"
+#include "base/task_runner.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/dbus/fake_session_manager_client.h"
@@ -32,6 +35,8 @@ namespace ash {
 namespace test {
 namespace {
 
+const int kWaitVolumeSliderHiddenInMs = 200;
+
 bool cursor_visible() {
   return Shell::GetInstance()->cursor_manager()->IsCursorVisible();
 }
@@ -41,6 +46,14 @@ void CheckCalledCallback(bool* flag) {
     (*flag) = true;
 }
 
+void WaitUntilVolumeSliderHidden() {
+  base::RunLoop run_loop;
+  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
+      FROM_HERE, run_loop.QuitClosure(),
+      base::TimeDelta::FromMilliseconds(kWaitVolumeSliderHiddenInMs));
+  run_loop.Run();
+}
+
 }  // namespace
 
 class LockStateControllerTest : public AshTestBase {
@@ -1050,6 +1063,7 @@ TEST_F(LockStateControllerTest, Screenshot) {
   PressPowerButton();
   ReleasePowerButton();
   ReleaseVolumeDown();
+  WaitUntilVolumeSliderHidden();
   EXPECT_EQ(1, delegate->handle_take_screenshot_count());
 }