- Validate that atomic ops can only be called when shared memory is declared
- Throw Compile/Link erros on mismatch between declared, imported memory
- Test harness helpers for setting shared memory, tests

BUG=v8:6532

R=binji@chromium.org, bradnelson@chromium.org

Change-Id: I43fe3d04bb7e3e0a2cecca0528578f98844d2608
Reviewed-on: https://chromium-review.googlesource.com/665379
Commit-Queue: Brad Nelson <bradnelson@chromium.org>
Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48019}