Use the correct method to map from paint invalidation container space to paint invalidation backing.

I noticed this small cleanup when working on the other CLs.

BUG=

Review URL: https://codereview.chromium.org/517913002

git-svn-id: svn://svn.chromium.org/blink/trunk@181110 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Update sheriff-o-matic's polymer version to 0.4.0.

The polymer versioning was broken. 0.3.3 no longer exists.
Workaround this by pulling 0.4.0. sheriff-o-matic.html and
run-unit-tests.html both seem to work fine, but "make test"
is broken. Not sure if it's related to the polymer change.

In either case, this at least gets people unstuck.

TBR=michaelpg@chromium.org

Review URL: https://codereview.chromium.org/521723002

git-svn-id: svn://svn.chromium.org/blink/trunk@181111 bbb929c8-8fbe-4397-9dbb-9b2b20218538