Use StopChildProcess instead of base::KillProcess to kill a renderer process

base::KillProcess doesn't work on android because a renderer process is running as an isolated process.
So we need to use StopChildProcess to kill it.

BUG=433068

Review URL: https://codereview.chromium.org/740813004

Cr-Commit-Position: refs/heads/master@{#306931}
24 files changed