[MD] simplify and unify some ink drop center calculations

ui/views/controls/button/label_button.cc

Index: ui/views/controls/button/label_button.cc
diff --git a/ui/views/controls/button/label_button.cc b/ui/views/controls/button/label_button.cc
index f192e1282b258644d0a913accb63245831b2b5e4..0f1bd6239ff4c95896c7ee75de85f4e9567d8ef5 100644
--- a/ui/views/controls/button/label_button.cc
+++ b/ui/views/controls/button/label_button.cc
@@ -420,8 +420,6 @@ void LabelButton::RemoveInkDropLayer(ui::Layer* ink_drop_layer) {
 
 scoped_ptr<views::InkDropAnimation> LabelButton::CreateInkDropAnimation()
     const {
-  // TODO(bruthig): Make the flood fill ink drops centered on the LocatedEvent
-  // that triggered them.
   return GetText().empty()
              ? CustomButton::CreateInkDropAnimation()
              : make_scoped_ptr(new views::FloodFillInkDropAnimation(
@@ -437,6 +435,13 @@ scoped_ptr<views::InkDropHover> LabelButton::CreateInkDropHover() const {
                    size(), 0, GetInkDropCenter(), GetInkDropBaseColor()));
 }
 
+gfx::Point LabelButton::GetInkDropCenter() const {
+  // TODO(bruthig): Make the flood fill ink drops centered on the LocatedEvent
+  // that triggered them.
+  return GetText().empty() ? image()->GetMirroredBounds().CenterPoint()

[sky, 2016/03/03 23:37:16]

It's worth a comment as to why this uses GetMirroredBounds.

[Evan Stade, 2016/03/04 04:07:52]

What comment content would you suggest? I sorta think the documentation of
GetMirroredBounds makes it obvious why it would be used in this case. Not sure
if you have a particular subtlety in mind that warrants clarifying.

[sky, 2016/03/04 16:37:29]

Ya, ok, fair enough.

[varkha, 2016/03/04 17:40:26]

What GetMirroredBounds does is indeed obvious here. There might still be room
for a comment here. In general case we want to target a center of a visible
button and an assumption made here is that a center of a visible portion of a
button is same as a center of the image when there is no text. Usually the image
is centered in a button but could be laid out differently when some inset is
reserved on a side to make a mouse target larger than a button.

[varkha, 2016/03/04 19:39:21]

Exactly, I would suggest something like:
"Some buttons have |bounds()| that expand past their visible bounds to make
targeting easier. Centering ink drop at the image center works for those buttons
but needs RTL mirroring to be positioned correctly."

+                           : CustomButton::GetInkDropCenter();
+}
+
 void LabelButton::StateChanged() {
   const gfx::Size previous_image_size(image_->GetPreferredSize());
   UpdateImage();