Make ant touch jar outputs

This prevents Gyp from performing unnecessary build actions due to Ant
not updating the modification time of the output when Gyp believes the
output is stale.

BUG=143229


Review URL: https://chromiumcodereview.appspot.com/10825403

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@152125 0039d316-1c4b-4281-b951-d872f2087c98

build/android/ant/chromium-jars.xml

@@ -65,6 +65,12 @@
     <!-- Create the distribution directory -->
     <mkdir dir="${lib.dir}" />
     <jar jarfile="${lib.dir}/chromium_${PACKAGE_NAME}.jar" basedir="${dest.dir}"/>
+
+    <!-- If Gyp thinks this output is stale but Ant doesn't, the modification
+         time should still be updated. Otherwise, this target will continue to
+         be rebuilt in future builds.
+    -->
+    <touch file="${lib.dir}/chromium_${PACKAGE_NAME}.jar"/>
   </target>
 
   <target name="clean" description="clean up">