Remove implicit conversions from scoped_refptr to T* in content/renderer/media/webrtc*

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

BUG=110610

Review URL: https://codereview.chromium.org/503683003

Cr-Commit-Position: refs/heads/master@{#292096}
16 files changed