Instrumented libraries: add a target for pre-built libraries.

Instrumented libraries: add a target for pre-built libraries.

With use_prebuilt_instrumented_libraries=1 in GYP_DEFINES, binaries are now
unpacked from archive and placed into output dir.

BUG=462636
R=glider@chromium.org
TBR=thakis@chromium.org
NOTRY=true

Committed: https://crrev.com/744256e2f3933feaa05c967541afac36825056fa
Cr-Commit-Position: refs/heads/master@{#321804}

[earthdok, 2015-03-18 21:49:39]

earthdok@chromium.org changed reviewers:
+ thakis@chromium.org

[earthdok, 2015-03-18 21:50:42]

Please take a look:

Alex - general review
Nico - ownership and possibly general review

[earthdok, 2015-03-18 21:53:40]

On 2015/03/18 21:50:42, earthdok wrote:
> Please take a look:
> 
> Alex - general review
> Nico - ownership and possibly general review

I unpack them into a separate directory because I don't want to bother with
cleanup in the event that the developer switches between two build types in the
same output dir. But I don't really like the word "prebuilt" - does anyone have
better ideas?

[Nico, 2015-03-20 17:35:39]

lgtm once glider is happy

[Nico, 2015-03-20 17:35:40]

lgtm once glider is happy

[Alexander Potapenko, 2015-03-23 12:43:47]

I am. LGTM

[earthdok, 2015-03-23 17:48:50]

The CQ bit was checked by earthdok@chromium.org

[commit-bot: I haz the power, 2015-03-23 17:49:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1017053003/20001

[commit-bot: I haz the power, 2015-03-23 17:50:17]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-23 17:51:18]

Patchset 2 (id:??) landed as
https://crrev.com/744256e2f3933feaa05c967541afac36825056fa
Cr-Commit-Position: refs/heads/master@{#321804}

[earthdok, 2015-03-23 17:55:07]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/1029103003/ by earthdok@chromium.org.

The reason for reverting is: Broke tree..