The JumpIfFalse and JumpIfTrue bytecodes test the accumulator, and
branch based on whether the accumulator is true or false (no other
value allowed, and in fact TurboFan would blow up if you would pass
anything else, since Branch operator can only deal with Boolean).
So for either branch we know exactly the value of the accumulator,
and we can update the environment to this constant value instead.

This helps to avoid the useless bit materialization that currently
happens when || or && is being used in a value context.

R=jarin@chromium.org
BUG=v8:5267

Review-Url: https://codereview.chromium.org/2666283002
Cr-Commit-Position: refs/heads/master@{#42843}