Cleanup some touch adjustment FIXMEs

This is a few little cleanups which I left behind as FIXMEs in previous
changes that were designed to be merge-worthy.  I don't believe any of
these changes should have an observable effect in real usage.
They are a pre-requisite, however, for additional fixes I intend to
make.

BUG=398914

Review URL: https://codereview.chromium.org/512983005

git-svn-id: svn://svn.chromium.org/blink/trunk@181672 bbb929c8-8fbe-4397-9dbb-9b2b20218538