There's no need to have the StringLengthProtector as a PropertyCell,
since it's only used to guard against deoptimization loops. This also
allows us to remove the use of the CompilationDependencies from the
JSTypedLowering.

R=jarin@chromium.org

Bug: v8:6759
Change-Id: I54a37be6b8064ca3475e3b321f928b6a9903f209
Tbr: mstarzinger@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/637303
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47633}