Hide dismiss button on toast when doing partial screenshot using stylus tools.

ash/common/system/toast/toast_overlay.h

 // Copyright 2016 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.
 
 #ifndef ASH_COMMON_SYSTEM_TOAST_TOAST_OVERLAY_H_
 #define ASH_COMMON_SYSTEM_TOAST_TOAST_OVERLAY_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
+#include "base/optional.h"
 #include "base/strings/string16.h"
 #include "ui/compositor/layer_animation_observer.h"
 #include "ui/events/event.h"
 #include "ui/events/event_constants.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace gfx {
 class Rect;
 }
 
@@ skipping 10 matching lines @@
 class ASH_EXPORT ToastOverlay : public ui::ImplicitAnimationObserver {
  public:
   class ASH_EXPORT Delegate {
    public:
     virtual ~Delegate() {}
     virtual void OnClosed() = 0;
   };
 
   // Creates the Toast overlay UI. |text| is the message to be shown, and
   // |dismiss_text| is the message for the button to dismiss the toast message.
-  // |dismiss_text| is optional. If empty, the default text is used.
+  // If |dismiss_text| is null, no dismiss button will be shown. If
+  // |dismiss_text| has a value but the string is empty, the default text is
+  // used.
   ToastOverlay(Delegate* delegate,
                const base::string16& text,
-               const base::string16& dismiss_text);
+               base::Optional<base::string16> dismiss_text);
   ~ToastOverlay() override;
 
   // Shows or hides the overlay.
   void Show(bool visible);
 
  private:
   friend class ToastManagerTest;
 
   // Returns the current bounds of the overlay, which is based on visibility.
   gfx::Rect CalculateOverlayBounds();
 
   // ui::ImplicitAnimationObserver:
   void OnImplicitAnimationsScheduled() override;
   void OnImplicitAnimationsCompleted() override;
 
   views::Widget* widget_for_testing();
+  ToastOverlayButton* dismiss_button_for_testing();
   void ClickDismissButtonForTesting(const ui::Event& event);
 
   Delegate* const delegate_;
   const base::string16 text_;
-  const base::string16 dismiss_text_;
+  const base::Optional<base::string16> dismiss_text_;
   std::unique_ptr<views::Widget> overlay_widget_;
   std::unique_ptr<ToastOverlayView> overlay_view_;
   gfx::Size widget_size_;
 
   DISALLOW_COPY_AND_ASSIGN(ToastOverlay);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TOAST_TOAST_OVERLAY_H_