This makes sure that {JSFunction} invocations always load the code start
address into the fixed {kJavaScriptCallCodeStartRegister} register. This
allows us to perform PC-relative operations more effective. For now this
only applies to code with {kCallJSFunction} linkage.

R=jarin@chromium.org

Change-Id: I16a32184c07f5e90b05114dff7530acf46c175f1
Reviewed-on: https://chromium-review.googlesource.com/888700
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51063}