Pressing spacebar on toolbar buttons triggers the ripple effect.

ui/views/controls/button/custom_button.cc

 // Copyright (c) 2012 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 "ui/views/controls/button/custom_button.h"
 
 #include "ui/accessibility/ax_view_state.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/events/event.h"
 #include "ui/events/event_utils.h"
@@ skipping 250 matching lines @@
 
 bool CustomButton::OnKeyPressed(const ui::KeyEvent& event) {
   if (state_ == STATE_DISABLED)
     return false;
 
   // Space sets button state to pushed. Enter clicks the button. This matches
   // the Windows native behavior of buttons, where Space clicks the button on
   // KeyRelease and Enter clicks the button on KeyPressed.
   if (event.key_code() == ui::VKEY_SPACE) {
     SetState(STATE_PRESSED);
+    if (ink_drop_delegate_ &&
+        ink_drop_delegate_->GetTargetInkDropState() !=
+            views::InkDropState::ACTION_PENDING)
+      ink_drop_delegate_->OnAction(views::InkDropState::ACTION_PENDING);
   } else if (event.key_code() == ui::VKEY_RETURN) {
     SetState(STATE_NORMAL);
     NotifyClick(event);
   } else {
     return false;
   }
   return true;
 }
 
 bool CustomButton::OnKeyReleased(const ui::KeyEvent& event) {
@@ skipping 227 matching lines @@
   Button::NotifyClick(event);
 }
 
 void CustomButton::OnClickCanceled(const ui::Event& event) {
   if (ink_drop_delegate())
     ink_drop_delegate()->OnAction(views::InkDropState::HIDDEN);
   Button::OnClickCanceled(event);
 }
 
 }  // namespace views