Support WebRTC in Android build toolchain

Support WebRTC in Android build toolchain

It turns out the changes in
https://codereview.chromium.org/17466002/ was not enough.
WebRTC needs two GYP_DEFINE variables to be passed to
the runhooks step in order to generate the right GYP
projects: include_tests=1 enable_tracing=1

We also need to use another build target than the default (All)
to compile only our tests.

This makes it possible to build the right APKs for
the Android Builder in the client.webrtc waterfall in:
https://codereview.chromium.org/17390019/

TEST=local builds
BUG=webrtc:1882
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=219016

[kjellander_chromium, 2013-08-21 09:49:41]

This now builds and runs the tests properly when I'm testing locally with a
device.

All that is left now is to fix copying of the resource files some of the tests
need. I think that should be handled by either adding .isolate files or listing
them in the GYP targets for the apk tests.

[Isaac (away), 2013-08-21 10:14:30]

lgtm.  I think this process barrier between bb_run_bot and bb_host_steps needs
to get removed --it's making all these CLs more complicated..

https://goto.google.com/zosmd

[commit-bot: I haz the power, 2013-08-22 09:13:38]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kjellander@chromium.org/23140007/14001

[commit-bot: I haz the power, 2013-08-22 14:22:27]

Change committed as 219016