The rounding error occured in VirtualMemory class when the provided page
allocator had bigger allocation page size than the commit page size and
the VirtualMemory was requested to reserve an area of a size aligned only
to commit page size.

Bug: v8:8096
Change-Id: Ifb9b7fe5797881408d1bb9e95073991a42b62e80
Reviewed-on: https://chromium-review.googlesource.com/c/1327041Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57365}