Pressing spacebar on toolbar buttons triggers the ripple effect.

ui/views/animation/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_INK_DROP_DELEGATE_H_
 #define UI_VIEWS_ANIMATION_INK_DROP_DELEGATE_H_
 
 #include "base/macros.h"
 #include "ui/views/animation/ink_drop_state.h"
 #include "ui/views/views_export.h"
@@ skipping 17 matching lines @@
   // enum.  The InkDropAction enum should be a subset of the InkDropState values
   // as well as a NONE value.
   virtual void OnAction(InkDropState state) = 0;
 
   // Immediately snaps the InkDropState to ACTIVATED.
   virtual void SnapToActivated() = 0;
 
   // Enables or disables the hover state.
   virtual void SetHovered(bool is_hovered) = 0;
 
+  // Returns the current InkDropState
+  virtual InkDropState GetTargetInkDropState() const = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(InkDropDelegate);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_ANIMATION_INK_DROP_DELEGATE_H_