Fix order of conversions in String.prototype.substr.

Fix order of conversions in String.prototype.substr.

The start argument must be converted to an integer before the length argument is
converted.  (Consequently, the start argument is converted even when the length
is 0.)  This matters because conversion is observable.

Also rewrite the function in a way that closely resembles the spec text.

R=littledan@chromium.org
BUG=v8:5140
Committed: https://crrev.com/f96be554b92a1e72eb524a43ad488d354ac0b603
Cr-Commit-Position: refs/heads/master@{#37378}

[Dan Ehrenberg, 2016-06-28 18:15:36]

lgtm

Much cleaner!

[neis, 2016-06-29 08:41:41]

The CQ bit was checked by neis@chromium.org

[neis, 2016-06-29 08:41:41]

The patchset sent to the CQ was uploaded after l-g-t-m from
littledan@chromium.org
Link to the patchset: https://codereview.chromium.org/2109583002/#ps20001
(title: "Get s.length only once.")

[commit-bot: I haz the power, 2016-06-29 08:41:56]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-06-29 09:51:44]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-06-29 09:54:01]

Description was changed from

==========
Fix order of conversions in String.prototype.substr.

The start argument must be converted to an integer before the length argument is
converted.  (Consequently, the start argument is converted even when the length
is 0.)  This matters because conversion is observable.

Also rewrite the function in a way that closely resembles the spec text.

R=littledan@chromium.org
BUG=v8:5140
==========

to

==========
Fix order of conversions in String.prototype.substr.

The start argument must be converted to an integer before the length argument is
converted.  (Consequently, the start argument is converted even when the length
is 0.)  This matters because conversion is observable.

Also rewrite the function in a way that closely resembles the spec text.

R=littledan@chromium.org
BUG=v8:5140

Committed: https://crrev.com/f96be554b92a1e72eb524a43ad488d354ac0b603
Cr-Commit-Position: refs/heads/master@{#37378}
==========

[commit-bot: I haz the power, 2016-06-29 09:54:02]

Patchset 2 (id:??) landed as
https://crrev.com/f96be554b92a1e72eb524a43ad488d354ac0b603
Cr-Commit-Position: refs/heads/master@{#37378}