Add MD ink drop ripple to shelf app items

ui/views/animation/ink_drop_host_view.cc

Index: ui/views/animation/ink_drop_host_view.cc
diff --git a/ui/views/animation/ink_drop_host_view.cc b/ui/views/animation/ink_drop_host_view.cc
index 49d59d64fd70f9971711f9a5fede98a095f02172..e3f721aacc02ba1706c29b9b74d586bf61e86be1 100644
--- a/ui/views/animation/ink_drop_host_view.cc
+++ b/ui/views/animation/ink_drop_host_view.cc
@@ -101,6 +101,7 @@ class InkDropHostView::InkDropGestureHandler : public ui::EventHandler {
 InkDropHostView::InkDropHostView()
     : ink_drop_(new InkDropStub()),
       ink_drop_size_(kInkDropSize, kInkDropSize),
+      old_paint_to_layer_(false),
       destroying_(false) {}
 
 InkDropHostView::~InkDropHostView() {
@@ -110,6 +111,7 @@ InkDropHostView::~InkDropHostView() {
 }
 
 void InkDropHostView::AddInkDropLayer(ui::Layer* ink_drop_layer) {
+  old_paint_to_layer_ = layer() != nullptr;
   SetPaintToLayer(true);
   layer()->SetFillsBoundsOpaquely(false);
   layer()->Add(ink_drop_layer);
@@ -123,7 +125,7 @@ void InkDropHostView::RemoveInkDropLayer(ui::Layer* ink_drop_layer) {
   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 {