Using the GraphBuilder base class forces each node creation to go
through a virtual function dispatch just for the sake of saving the
duplication of the NewNode helper methods. In total that added up to
saving minus (sic!) six lines of code.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/1252093002

Cr-Commit-Position: refs/heads/master@{#29799}