[turbofan] Fix pushing of JSToBooleans into Phis.

[turbofan] Fix pushing of JSToBooleans into Phis.

Now we actually implement it the way it is meant to be, that is:

  JSToBoolean(Phi(x1,...,xn):primitive)
    => Phi(JSToBoolean(x1),...,JSToBoolean(xn)):boolean

This also fixes the endless recursion within JSTypedLowering when
the GraphReducer does all possible reductions instead of using the
generic algorithm.

R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/730043002

Cr-Commit-Position: refs/heads/master@{#25376}