Avoid modifying the real context chain for debug evaluation.

Avoid modifying the real context chain for debug evaluation.

Instead of modifying a context chain and then modifying it back, causing
potential mismatches, we clone the inner context chain and evaluate
the expression in this cloned context. We then copy all local variable
values back if needed.

R=yangguo@chromium.org,yurys@chromium.org

Committed: https://crrev.com/219f4a9eb42b14563ce4c4930770dd74d0dde5f8
Cr-Commit-Position: refs/heads/master@{#27809}

[Dmitry Lomov (no reviews), 2015-04-13 14:06:07]

ptal

[Dmitry Lomov (no reviews), 2015-04-13 14:08:52]

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

[commit-bot: I haz the power, 2015-04-13 14:09:00]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1088503003/20001

[commit-bot: I haz the power, 2015-04-13 14:12:34]

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

[commit-bot: I haz the power, 2015-04-13 14:12:36]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/1944)

[Dmitry Lomov (no reviews), 2015-04-14 07:52:00]

ping

[Yang, 2015-04-14 09:06:10]

lgtm

[Dmitry Lomov (no reviews), 2015-04-14 09:06:28]

The CQ bit was checked by dslomov@chromium.org

[commit-bot: I haz the power, 2015-04-14 09:06:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1088503003/20001

[commit-bot: I haz the power, 2015-04-14 09:08:07]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-14 09:08:19]

Patchset 2 (id:??) landed as
https://crrev.com/219f4a9eb42b14563ce4c4930770dd74d0dde5f8
Cr-Commit-Position: refs/heads/master@{#27809}