Remove implicit conversions from scoped_refptr to T* in gpu/

This patch was generated by running the rewrite_scoped_refptr clang tool
on a Linux build.

BUG=110610
R=sievers@chromium.org

Review URL: https://codereview.chromium.org/500243002

Cr-Commit-Position: refs/heads/master@{#291805}
18 files changed