Pressing spacebar on toolbar buttons triggers the ripple effect.

ui/views/animation/button_ink_drop_delegate.h

 // Copyright 2015 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 UI_VIEWS_ANIMATION_BUTTON_INK_DROP_DELEGATE_H_
 #define UI_VIEWS_ANIMATION_BUTTON_INK_DROP_DELEGATE_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 23 matching lines @@
     return last_ink_drop_location_;
   }
   void set_last_ink_drop_location(const gfx::Point& point) {
     last_ink_drop_location_ = point;
   }
 
   // InkDropDelegate:
   void OnAction(InkDropState state) override;
   void SnapToActivated() override;
   void SetHovered(bool is_hovered) override;
+  InkDropState GetTargetInkDropState() const override;
 
   // ui::EventHandler:
   void OnMouseEvent(ui::MouseEvent* event) override;
   void OnGestureEvent(ui::GestureEvent* event) override;
 
  private:
   // An instance of ScopedTargetHandler allowing |this| to handle events.
   std::unique_ptr<ui::ScopedTargetHandler> target_handler_;
 
   // Parent InkDropHost (typically a View) that hosts the ink ripple animations.
   InkDropHost* ink_drop_host_;
 
   // Location of the last ink drop triggering event in coordinate system of the
   // ctor argument |view|.
   gfx::Point last_ink_drop_location_;
 
   // Animation controller for the ink drop ripple effect.
   std::unique_ptr<InkDrop> ink_drop_;
 
   DISALLOW_COPY_AND_ASSIGN(ButtonInkDropDelegate);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_ANIMATION_BUTTON_INK_DROP_DELEGATE_H_