Fix heuristics to prefer precise GCs more and avoid repeated GCs on tiny heaps

R=ager@chromium.org, haraken@chromium.org, zerny@chromium.org, sigbjornf@opera.com
BUG=374431

Review URL: https://codereview.chromium.org/291303005

git-svn-id: svn://svn.chromium.org/blink/trunk@174453 bbb929c8-8fbe-4397-9dbb-9b2b20218538