Fix some nits as a follow-up for issue 355193003.

BUG=381876
TBR=haraken

Review URL: https://codereview.chromium.org/360053004

git-svn-id: svn://svn.chromium.org/blink/trunk@177247 bbb929c8-8fbe-4397-9dbb-9b2b20218538
MSE: Complete removal of Blink-side support for LegacyFrameProcessor

This is the last of a three-sided change to remove LegacyFrameProcessor
from Blink and Chromium now that the new FrameProcessor is stabilized.

R=acolwell@chromium.org,abarth@chromium.org
BUG=249422
TEST=No MSE layout test regression locally on Linux

Review URL: https://codereview.chromium.org/309933002

git-svn-id: svn://svn.chromium.org/blink/trunk@177248 bbb929c8-8fbe-4397-9dbb-9b2b20218538