Fix messages tests.

Change tests so that message location is stable under --debug-code.

R=yangguo@chromium.org
BUG=v8:3744
LOG=N

Review URL: https://codereview.chromium.org/792563003

Cr-Commit-Position: refs/heads/master@{#25732}
Pass --noharmony-scoping to tests validating that we throw on 'const' in strict mode.

R=marja@chromium.org
BUG=v8:2198
LOG=N

Review URL: https://codereview.chromium.org/784323002

Cr-Commit-Position: refs/heads/master@{#25733}
Rename shadowing `pos` variable in ParseTemplateLiteral()

LOG=N
R=dslomov@chromium.org
BUG=

Review URL: https://codereview.chromium.org/785233005

Cr-Commit-Position: refs/heads/master@{#25734}
Add Array.prototype.includes

Requires adding a SameValueZero implementation.

LOG=Y
BUG=v8:3575
R=dslomov@chromium.org, arv@chromium.org
TEST=added to test262

Review URL: https://codereview.chromium.org/771863002

Cr-Commit-Position: refs/heads/master@{#25735}