If a new code allocation request cannot be fulfilled, do not just
reserve enough to fulfill this one request, but request at least 20
percent of the total reserved code space so far. This ensures that
the reserved space grows exponentially instead of linearly.

R=mstarzinger@chromium.org

Bug: chromium:987560
Change-Id: I3fc4dd0f7acee2a380495a87c0425c58058551bc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1718144Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62910}