Add MD ink drop ripple to shelf app items

ui/views/animation/ink_drop_host_view.cc

 // 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.
 
 #include "ui/views/animation/ink_drop_host_view.h"
 
 #include "ui/events/event.h"
 #include "ui/events/scoped_target_handler.h"
 #include "ui/gfx/color_palette.h"
 #include "ui/gfx/geometry/size_conversions.h"
@@ skipping 83 matching lines @@
 
   // An instance of ScopedTargetHandler allowing |this| to handle events.
   ui::ScopedTargetHandler target_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(InkDropGestureHandler);
 };
 
 InkDropHostView::InkDropHostView()
     : ink_drop_(new InkDropStub()),
       ink_drop_size_(kInkDropSize, kInkDropSize),
+      old_paint_to_layer_(false),
       destroying_(false) {}
 
 InkDropHostView::~InkDropHostView() {
   // TODO(bruthig): Improve InkDropImpl to be safer about calling back to
   // potentially destroyed InkDropHosts and remove |destroying_|.
   destroying_ = true;
 }
 
 void InkDropHostView::AddInkDropLayer(ui::Layer* ink_drop_layer) {
+  old_paint_to_layer_ = layer() != nullptr;
   SetPaintToLayer(true);
   layer()->SetFillsBoundsOpaquely(false);
   layer()->Add(ink_drop_layer);
   layer()->StackAtBottom(ink_drop_layer);
 }
 
 void InkDropHostView::RemoveInkDropLayer(ui::Layer* ink_drop_layer) {
   // No need to do anything when called during shutdown, and if a derived
   // class has overridden Add/RemoveInkDropLayer, running this implementation
   // would be wrong.
   if (destroying_)
     return;
   layer()->Remove(ink_drop_layer);
-  SetPaintToLayer(false);
+  SetPaintToLayer(old_paint_to_layer_);

[bruthig, 2016/06/09 03:26:00]

What's the use case for this?

[mohsen, 2016/06/09 21:24:51]

I think if a View had already been painting to layer before ink drop layer was
added (e.g. ShelfButton), we should not set paint-to-layer false here.
Otherwise, it might break things!

PS: ShelfButton is set to paint to layer in ShelfView::Init().

[bruthig, 2016/06/10 15:25:19]

Hmm VERY good point! It seems that this SetPaintToLayer() method is enabling
distributed ownership of whether the View should paint to a layer or not and is
tough to reason about and get correct.  Can you add a TODO, perhaps on
View::SetPaintToLayer(), to consider making it more robust for these use cases?
e.g. Adding a counter and only destroying the layer when the count gets to 0.

This change looks good for this CL though.

 }
 
 std::unique_ptr<InkDropRipple> InkDropHostView::CreateInkDropRipple() const {
   std::unique_ptr<InkDropRipple> ripple(new SquareInkDropRipple(
       CalculateLargeInkDropSize(ink_drop_size_), kInkDropLargeCornerRadius,
       ink_drop_size_, kInkDropSmallCornerRadius, GetInkDropCenter(),
       GetInkDropBaseColor()));
   return ripple;
 }
 
@@ skipping 53 matching lines @@
     gesture_handler_.reset();
     ink_drop_.reset(new InkDropStub());
   }
 }
 
 void InkDropHostView::AnimateInkDrop(InkDropState ink_drop_state) {
   ink_drop_->AnimateToState(ink_drop_state);
 }
 
 }  // namespace views