Allow win_ash to build with only use_ash defined.

BUG=none
TEST=none
Review URL: https://chromiumcodereview.appspot.com/10379015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@135417 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/build/common.gypi b/build/common.gypi
index 5716e61..c11bca5 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -88,6 +88,9 @@
           ['use_aura==1 and ((OS=="linux" and chromeos==0) or OS=="win")', {
             'use_ash%': 1,
           }],
+          ['use_ash==1', {
+            'use_aura%': 1,
+          }],
 
           # Set default value of toolkit_views based on OS.
           ['OS=="win" or chromeos==1 or use_aura==1', {