Mark SkBBoxHierarchyRecord destructor as virtual

Immediate parent classes have empty virtual destructors, but farther
up the inheritance tree there is complicated destruction going on.
This change may be unnecessary but makes the polymorphism explicit.

BUG=skia:1734
R=mtklein@google.com, tomhudson@google.com, mtklein

Author: tomhudson@chromium.org

Review URL: https://codereview.chromium.org/359773002
1 file changed