Plugin Power Saver: Replace all "plug-in" with "plugin" for consistency.

Passed chrome-ui-review: https://groups.google.com/a/google.com/d/msg/chrome-ui-review/FwuQ2TWc5n8/H3PSuV4L_cAJ

BUG=467165

TBR=tsepez
(comment changes only in render_messages)

NOPRESUBMIT=true
(legacy LOG messages)

Review URL: https://codereview.chromium.org/1007443004

Cr-Commit-Position: refs/heads/master@{#320782}
126 files changed