[es6] Fix parsing of 'yield' in function and generator expressions

[es6] Fix parsing of 'yield' in function and generator expressions

In a function expression, 'yield' is allowed, even if the expression
occurs inside a generator. Similarly, even in a non-generator,
a generator expression's name must not be 'yield'.

BUG=v8:3983
LOG=n

Committed: https://crrev.com/2ea7f3c8690e51e15147493b468a9837ab980bf3
Cr-Commit-Position: refs/heads/master@{#32188}

[adamk, 2015-11-21 00:48:11]

adamk@chromium.org changed reviewers:
+ littledan@chromium.org, wingo@igalia.com

[Dan Ehrenberg, 2015-11-23 19:48:45]

lgtm

[adamk, 2015-11-23 21:00:34]

The CQ bit was checked by adamk@chromium.org

[commit-bot: I haz the power, 2015-11-23 21:00:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1460393003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1460393003/1

[commit-bot: I haz the power, 2015-11-23 21:34:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-23 21:34:34]

Patchset 1 (id:??) landed as
https://crrev.com/2ea7f3c8690e51e15147493b468a9837ab980bf3
Cr-Commit-Position: refs/heads/master@{#32188}