views: implement width snapping for DialogDelegateViews

ui/views/views_delegate.h

Index: ui/views/views_delegate.h
diff --git a/ui/views/views_delegate.h b/ui/views/views_delegate.h
index 5ab30aa42997cf7bb298dcdf71caab5b07eb9c29..4b9b01f2f65940a59229dbe757ac191637937eda 100644
--- a/ui/views/views_delegate.h
+++ b/ui/views/views_delegate.h
@@ -257,6 +257,10 @@ class VIEWS_EXPORT ViewsDelegate {
   // font, weight, color, size, and line height. Never null.
   virtual const TypographyProvider& GetTypographyProvider() const = 0;
 
+  // Returns the smallest dialog width that can contain a dialog whose unsnapped
+  // width is |width|.
+  virtual int GetSnappedDialogWidth(int width) const;
+
  protected:
   ViewsDelegate();