Add AS to scons_import_variables and scons_propagate_variables.

Review URL: http://codereview.chromium.org/99292

git-svn-id: http://src.chromium.org/svn/trunk/src/build@15086 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -229,11 +229,13 @@
           ],
         },
         'scons_import_variables': [
+          'AS',
           'CC',
           'CXX',
           'LINK',
         ],
         'scons_propagate_variables': [
+          'AS',
           'CC',
           'CCACHE_DIR',
           'CXX',