For fullcodegen the RuntimeProfiler has a shortcut that allows it to
tier up small functions earlier, when enough type feedback is available.
Port the same optimization for the Ignition+TurboFan pipeline.

R=mstarzinger@chromium.org

Review-Url: https://chromiumcodereview.appspot.com/2427283004
Cr-Commit-Position: refs/heads/master@{#40435}