GeneratorFunction() makes generator instances

GeneratorFunction() makes generator instances

The current specification has GeneratorFunction() be like Function(),
except that it makes generator instances.  This commit implements that
behavior.  It also fills in a piece of the implementation where
otherwise calling GeneratorFunction or GeneratorFunctionPrototype would
cause an abort because they have no code.

R=mstarzinger@chromium.org
TEST=mjsunit/harmony/generators-iteration
TEST=mjsunit/harmony/generators-runtime
BUG=v8:2355, v8:2680
Committed: http://code.google.com/p/v8/source/detail?r=15084

[wingo, 2013-05-16 09:45:26]

This is another attempt to land https://codereview.chromium.org/14857009/, this
time making it so that SyntaxErrors are raised from the constructor itself and
not a helper.  Except for the paren error, anyway.  Hopefully that fixes the WK
layout tests, though I haven't tried.

We might want to wait until after the roll for this one.

[Michael Starzinger, 2013-05-23 08:32:11]

LGTM.

[wingo, 2013-06-12 12:47:25]

I had wanted to wait until the WebKit bot was green, but as discussed offline it
seems this isn't happening.  Instead I'll land and watch the webkit tests for
diffs.

[wingo, 2013-06-12 12:52:25]

Committed patchset #1 manually as r15084 (presubmit successful).