Fix STEP_WARNINGS for android buildbot

Fix STEP_WARNINGS for android buildbot

- bb_goma_make does not return the exit status of make
  due to the goma shutdown step.
  For bb_compile_experimental, bash exit on error is disabled
  and we are relying on bb_goma_make exit status to determine
  failure.

BUG=
TEST=


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=142111

[Isaac (away), 2012-06-14 07:41:26]

Locally tested

http://levy.mtv:8011/builders/Chromium%20Linux%20Android%20Builder/builds/19

[Isaac (away), 2012-06-14 07:42:53]

Copy and paste the link instead of clicking

[bulach, 2012-06-14 07:46:19]

lgtm, thanks!

[commit-bot: I haz the power, 2012-06-14 07:46:52]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ilevy@chromium.org/10536165/1

[commit-bot: I haz the power, 2012-06-14 08:48:59]

Change committed as 142111

[John Grabowski, 2012-06-14 18:27:51]

LGTM