This CL is part of the effort to remove the usage of 'ebx' as it will
be the kRootRegister on ia32.

R=jgruber@chromium.org

Bug: v8:6666
Change-Id: Iad3d4718423a22790908d5028b2ec9e8b2253126
Reviewed-on: https://chromium-review.googlesource.com/1233258Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Simon Zünd <szuend@google.com>
Cr-Commit-Position: refs/heads/master@{#56023}