Allow dialogs to use a custom View as their title.

ui/views/window/dialog_delegate.cc

Index: ui/views/window/dialog_delegate.cc
diff --git a/ui/views/window/dialog_delegate.cc b/ui/views/window/dialog_delegate.cc
index 0d6b99feb73e0b14e0847749f4648b02f516d154..ea3c42dfa82d9a1972d6c33df823608e271d9a08 100644
--- a/ui/views/window/dialog_delegate.cc
+++ b/ui/views/window/dialog_delegate.cc
@@ -91,8 +91,12 @@ Widget::InitParams DialogDelegate::GetDialogWidgetInitParams(
   return params;
 }
 
+StyledLabel* DialogDelegate::CreateTitleView() {
+  return nullptr;

[Peter Kasting, 2017/06/07 02:40:43]

Why not have this return a StyledLabel for GetWindowTitle()?

Then the caller doesn't need to worry about checking one or the other, it can
just check this.

Where I'd like to go with this is to make GetWindowTitle() private -- so the
window title is only exposed to callers through this method.  There aren't that
many callers of it today.  However, looking at that highlights that
DialogDelegate::GetAccessibleNodeData() assumes it can read the window title
from GetWindowTitle().  If a class overrides CreateTitleView() and doesn't also
provide a parallel accessible version in GetWindowTitle(), they'll do the wrong
thing.

If GetAccessibleNodeData() read the text out of the label returned here, that
would work; but returning a new label each time just to read the data seems bad.
 If DialogDelegate owned the StyledLabel and CreateTitleView() just updated the
member, we could access that way; but proper ownership becomes a bit of an issue
then (probably the view has to be unique_ptr'd to this class and
set_owned_by_parent(false), and I don't know if that can cause destruction order
issues).

Still, I don't have a better idea unless you want to limit this entirely to
BubbleFrameView.

[Bret, 2017/06/07 20:15:41]

I'll keep this in mind as I rework it, and see if I can find a way to enforce
that the label title matches GetWindowTitle (even if it's just with a DCHECK).

+}
+
 View* DialogDelegate::CreateExtraView() {
-  return NULL;
+  return nullptr;
 }
 
 bool DialogDelegate::GetExtraViewPadding(int* padding) {