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: svn://svn.chromium.org/chrome/trunk/src@40229 0039d316-1c4b-4281-b951-d872f2087c98

build/all.gyp

@@ -234,11 +234,16 @@
         {
           'target_name': 'chromeos_builder',
           'type': 'none',
+          'sources': [
+            # TODO(bradnelson): This is here to work around gyp issue 137.
+            #     Remove this sources list when that issue has been fixed.
+            'all.gyp',
+          ],
           'dependencies': [
             '../chrome/chrome.gyp:chrome',
             '../media/media.gyp:omx_test',
             '../media/media.gyp:ffmpeg_tests',
-	    # TODO(jiesun): should we put candidate_window/session here?
+            # TODO(jiesun): should we put candidate_window/session here?
           ],
         },
       ],  # targets