Telemetry: Keep original exception's stacktrace in inspector_backend.

Telemetry: Keep original exception's stacktrace in inspector_backend.

InspectorBackend converts exceptions generated by the websocket library into
Telemetry exceptions. In the process, it was losing the original stacktrace.

BUG=NONE

Committed: https://crrev.com/72bf8d182a23c36614fd049c276d6a34e991cc02
Cr-Commit-Position: refs/heads/master@{#319821}

[erikchen, 2015-03-10 00:16:44]

erikchen@chromium.org changed reviewers:
+ dtu@chromium.org

[erikchen, 2015-03-10 00:16:44]

dtu: Please review.

[dtu, 2015-03-10 00:23:48]

Great! I knew there was some place where we needed this fix. Glad you found it!
lgtm

[erikchen, 2015-03-10 00:25:54]

The CQ bit was checked by erikchen@chromium.org

[commit-bot: I haz the power, 2015-03-10 00:26:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/990153003/1

[commit-bot: I haz the power, 2015-03-10 02:14:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-10 02:14:50]

Patchset 1 (id:??) landed as
https://crrev.com/72bf8d182a23c36614fd049c276d6a34e991cc02
Cr-Commit-Position: refs/heads/master@{#319821}