Fix ASSERTION FAILED: roundedIntPoint(rendererMappedResult) == roundedIntPoint(result).

This is the exact same situation as https://codereview.chromium.org/27104002/, I just
missed a codepath the first time.

Basically, the ASSERT shouldn't be applied to invisible layers, we expect them to
have this mismatch.

BUG=264634

Review URL: https://codereview.chromium.org/92813002

git-svn-id: svn://svn.chromium.org/blink/trunk@162797 bbb929c8-8fbe-4397-9dbb-9b2b20218538