Rename String.prototype.contains to 'includes'.

Per TC39 Nov 2014 decison.

R=arv@chromium.org,yangguo@chromium.org
LOG=Y

Committed: https://chromium.googlesource.com/v8/v8/+/b5379216e23ff0ec734e70361dd07057c2421c96

Review URL: https://codereview.chromium.org/742963002

Cr-Commit-Position: refs/heads/master@{#25448}
Do not put D8 and TEST natives into the external snapshot.

D8 natives, in particular, will cause Windows static builds to not link due to another definition in the generated file d8-js.cc.

BUG=421063

Review URL: https://codereview.chromium.org/738153003

Cr-Commit-Position: refs/heads/master@{#25449}