Remove implicit conversions from scoped_refptr to T* in net/

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

BUG=110610

Review URL: https://codereview.chromium.org/509563003

Cr-Commit-Position: refs/heads/master@{#292233}
12 files changed