Add BoxF::ExpandTo

ui/gfx/box_f.h

Index: ui/gfx/box_f.h
diff --git a/ui/gfx/box_f.h b/ui/gfx/box_f.h
index fb2c1910a96ebe18375ab8eee821f136ea0b51a5..11770ee58acaa224a3d4984dd8ab2b9d7faa6fcc 100644
--- a/ui/gfx/box_f.h
+++ b/ui/gfx/box_f.h
@@ -94,7 +94,20 @@ class GFX_EXPORT BoxF {
   const Point3F& origin() const { return origin_; }
   void set_origin(const Point3F& origin) { origin_ = origin; }
 
+  // Expands |this| to contain the given point, if necessary. Please note, even
+  // if |this| is empty, after the function |this| will continue to contain its
+  // |origin_|.
+  void ExpandTo(const Point3F& point);
+
  private:
+  // Expands the box to contain the two given points. It is required that each
+  // component of |min| is less than or equal to the corresponding component in
+  // |max|. Precisely, what this function does is ensure that after the function
+  // completes, |this| contains origin_, min, max, and origin_ + (width_,
+  // height_, depth_), even if the box is empty. Emptiness checks are handled in
+  // the public function Union.
+  void ExpandTo(const Point3F& min, const Point3F& max);
+
   Point3F origin_;
   float width_;
   float height_;