When memory.grow was executed concurrently on multiple threads a data
race could happen such that two memory.grow operations result in the
same return value. With this CL the return value of memory.grow is
unique, given that memory.grow actually grows the memory.

As a concrete example, assume a shared WebAssembly memory initially has
a size of 100. Assume two threads call memory.grow concurrently with a
parameter `10`. Then with the existing code, memory would grow correctly
to a size of 120, but the data race may cause both memory.grow
operations to return 100. With the change in this CL one memory.grow
operation would return 100, the other would return 110.

R=gdeepti@chromium.org
CC=rreverser@google.com

Bug: chromium:1067621
Change-Id: Ib22b5135714a56799e0818ccb39e5dce327e5f8e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144113Reviewed-by: Ben Smith <binji@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67135}