Do not eagerly convert exception to string when creating a message object

Do not eagerly convert exception to string when creating a message object

R=mstarzinger@chromium.org
BUG=chromium:490680
LOG=Y

Committed: https://crrev.com/36d8363c1cace489cbccfedcf3777863b12d4887
Cr-Commit-Position: refs/heads/master@{#28670}

[Yang, 2015-05-22 09:34:37]

The CQ bit was checked by yangguo@chromium.org to run a CQ dry run

[Yang, 2015-05-22 09:34:48]

The CQ bit was unchecked by yangguo@chromium.org

[Michael Starzinger, 2015-05-22 16:18:39]

LGTM.

https://codereview.chromium.org/1157563005/diff/20001/test/mjsunit/regress/re...
File test/mjsunit/regress/regress-crbug-490680.js (right):

https://codereview.chromium.org/1157563005/diff/20001/test/mjsunit/regress/re...
test/mjsunit/regress/regress-crbug-490680.js:10: }
Can we also add the following construct to the test case?

L: try {
  throw { toString: function() { sentinel = "observed"; } };
} finally {
  break L;
}

[Yang, 2015-05-27 13:43:38]

The CQ bit was checked by yangguo@chromium.org to run a CQ dry run

[Yang, 2015-05-27 13:43:39]

The patchset sent to the CQ was uploaded after l-g-t-m from
mstarzinger@chromium.org
Link to the patchset: https://codereview.chromium.org/1157563005/#ps100001
(title: "small change")

[Yang, 2015-05-27 13:43:43]

The CQ bit was unchecked by yangguo@chromium.org

[Yang, 2015-05-27 14:00:59]

The CQ bit was checked by yangguo@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-05-27 14:01:10]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1157563005/100001

[commit-bot: I haz the power, 2015-05-27 14:32:04]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-27 14:32:05]

Dry run: This issue passed the CQ dry run.

[Yang, 2015-05-28 06:28:05]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-05-28 06:28:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1157563005/100001

[commit-bot: I haz the power, 2015-05-28 06:30:13]

Committed patchset #6 (id:100001)

[commit-bot: I haz the power, 2015-05-28 06:30:26]

Patchset 6 (id:??) landed as
https://crrev.com/36d8363c1cace489cbccfedcf3777863b12d4887
Cr-Commit-Position: refs/heads/master@{#28670}