This is a first step towards explicit checkpoints in the graph. For now
we still use the explicit eager bailout points in the AstGraphBuilder
that are marked by the FrameStateBeforeAndAfter helper. Eventually these
will be implicitly emitted by expression visits having a side-effect.

R=bmeurer@chromium.org
BUG=v8:5021

Review-Url: https://codereview.chromium.org/2018403002
Cr-Commit-Position: refs/heads/master@{#36638}