Working around gyp issue 137 in scons emitter. The scons generator currently does not correctly handle the case in which you have a target with no sources (for instance all the mock targets used for the bots). So far this has not been an issue because these mock targets were only used for Windows and Mac. jiesun's recent addition of a chromeos_builder target caused this issue to manifest itself.
Working around gyp issue 137 in scons emitter.
The scons generator currently does not correctly handle the case in which you
have a target with no sources (for instance all the mock targets used for the
bots). So far this has not been an issue because these mock targets were only
used for Windows and Mac. jiesun's recent addition of a chromeos_builder target
caused this issue to manifest itself.

BUG=None
TEST=None
TBR=jiesuN

Review URL: http://codereview.chromium.org/661249

git-svn-id: http://src.chromium.org/svn/trunk/src@40229 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 24f5fc1b4a398a24e7c1d1226d4a8176e0ce49ba
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser