Add ink drop ripple to overview mode button

ui/views/animation/ink_drop_impl.cc

 // 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.
 
 #include "ui/views/animation/ink_drop_impl.h"
 
 #include "base/auto_reset.h"
 #include "base/timer/timer.h"
 #include "ui/compositor/layer.h"
 #include "ui/views/animation/ink_drop_highlight.h"
@@ skipping 689 matching lines @@
 
 void InkDropImpl::AnimationStarted(InkDropState ink_drop_state) {
   highlight_state_->AnimationStarted(ink_drop_state);
 }
 
 void InkDropImpl::AnimationEnded(InkDropState ink_drop_state,
                                  InkDropAnimationEndedReason reason) {
   highlight_state_->AnimationEnded(ink_drop_state, reason);
   if (reason != InkDropAnimationEndedReason::SUCCESS)
     return;
+  // |ink_drop_ripple_| might be null during destruction.
+  if (!ink_drop_ripple_)

[bruthig, 2016/11/11 17:30:40]

Can you add an InkDropImpl specific test for this?
Check out InkDropImplHideAutoHighlightTest.NoCrashDuringRippleTearDown.  You
will probably want to use the ZERO duration animation setting to force this use
case.

[mohsen, 2016/11/11 22:37:24]

Done.

+    return;
   if (ShouldAnimateToHidden(ink_drop_state)) {
     ink_drop_ripple_->AnimateToState(views::InkDropState::HIDDEN);
   } else if (ink_drop_state == views::InkDropState::HIDDEN) {
     // TODO(bruthig): Investigate whether creating and destroying
     // InkDropRipples is expensive and consider creating an
     // InkDropRipplePool. See www.crbug.com/522175.
     DestroyInkDropRipple();
   }
 }
 
@@ skipping 49 matching lines @@
                                        "within a call to "
                                        "HighlightState::Exit().";
   if (highlight_state_) {
     base::AutoReset<bool> exit_guard(&exiting_highlight_state_, true);
     highlight_state_->Exit();
   }
   highlight_state_ = nullptr;
 }
 
 }  // namespace views