Add AS to scons_import_variables and scons_propagate_variables.

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

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@15086 0039d316-1c4b-4281-b951-d872f2087c98

build/common.gypi

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