Fix external callback logging in profiler.

Fix external callback logging in profiler.

For platforms that use function descriptors (currently AIX and
PPC64BE), log an external callback's entrypoint address rather than
its function descriptor address.  This allows proper lookup in the
tick processor's symbol table.

R=jkummerow@chromium.org, michael_dawson@ca.ibm.com
BUG=

Committed: https://crrev.com/2bd5914bc3ae8c01c115f0386ae91c9f341c7ccb
Cr-Commit-Position: refs/heads/master@{#31633}

[MTBrandyberry, 2015-10-27 18:08:31]

This fix is part of the solution for an issue found in node.js testing.

(see https://github.com/nodejs/node/issues/2957)

[Jakob Kummerow, 2015-10-28 09:21:47]

lgtm

[MTBrandyberry, 2015-10-28 13:17:35]

The CQ bit was checked by mbrandy@us.ibm.com

[commit-bot: I haz the power, 2015-10-28 13:17:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1409993006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1409993006/1

[commit-bot: I haz the power, 2015-10-28 13:42:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-28 13:42:49]

Patchset 1 (id:??) landed as
https://crrev.com/2bd5914bc3ae8c01c115f0386ae91c9f341c7ccb
Cr-Commit-Position: refs/heads/master@{#31633}