[debugger] Make Runtime_DebugEvaluate safe for reentry.

[debugger] Make Runtime_DebugEvaluate safe for reentry.

Only one FrameInspector can be active at a time on any given stack,
this ensures that it's lifetime is sufficiently scoped.

R=yangguo@chromium.org
TEST=mjsunit/regress/regress-crbug-259300

Committed: https://crrev.com/fced43a6862ec8b8743951ae044fe43427834d3f
Cr-Commit-Position: refs/heads/master@{#27477}

[Yang, 2015-03-26 10:00:02]

On 2015/03/25 15:56:13, Michael Starzinger wrote:

lgtm!

[Michael Starzinger, 2015-03-26 12:27:53]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-03-26 12:27:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1034743002/1

[commit-bot: I haz the power, 2015-03-26 12:30:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-26 12:31:16]

Patchset 1 (id:??) landed as
https://crrev.com/fced43a6862ec8b8743951ae044fe43427834d3f
Cr-Commit-Position: refs/heads/master@{#27477}