Fix support for mojo_common_unittests on MSan.

Fix support for mojo_common_unittests on MSan.

This broke in 194f4c6bea6ae714cfa6a0eb32bf7e79a70e0192.

MSan uses libc++ on Linux, unlike the normal build, so libc++.so must be mapped.
It is mapped as part of base.isolate.

R=jam@chromium.org
BUG=98637
Committed: https://crrev.com/6fdafbf5e1ca5fbe4e9357c25978906453557225
Cr-Commit-Position: refs/heads/master@{#338760}

[eugenis, 2015-07-14 19:56:25]

eugenis@chromium.org changed reviewers:
+ eugenis@chromium.org

[eugenis, 2015-07-14 19:56:25]

lgtm

[jam, 2015-07-14 20:20:10]

lgtm

[M-A Ruel, 2015-07-14 20:51:08]

The CQ bit was checked by maruel@chromium.org

[commit-bot: I haz the power, 2015-07-14 20:51:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1235673004/1

[commit-bot: I haz the power, 2015-07-14 22:39:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-14 22:40:33]

Patchset 1 (id:??) landed as
https://crrev.com/6fdafbf5e1ca5fbe4e9357c25978906453557225
Cr-Commit-Position: refs/heads/master@{#338760}