Check variable PRODUCT_DIR firstly for content shell test

content/shell/android/javatests/content_shell_test_apk.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!--
   Copyright (c) 2012 The Chromium Authors. All rights reserved.
   Use of this source code is governed by a BSD-style license that can be
   found in the LICENSE file.
 -->
 <project name="ContentShellTest" default="debug" basedir=".">
 
   <description>
     Building ContentShellTest.apk
@@ skipping 15 matching lines @@
   <property name="asset.absolute.dir" location="${out.dir}/assets" />
 
   <path id="out.dex.jar.input.ref">
     <fileset dir="${PRODUCT_DIR}/content_shell/java/libs"/>
     <pathelement location="${PRODUCT_DIR}/content_shell/classes"/>
   </path>
   <property name="java.compilerargs" value="-classpath ${toString:out.dex.jar.input.ref}"/>
 
   <!-- We expect PRODUCT_DIR to be set like the gyp var
        (e.g. $ROOT/out/Debug) -->
-  <!-- TODO(satish): ideally we need this to run before -build-setup, where
-       directories are made based on this variable. -->
-  <target name="-pre-build">
-    <if>
-      <condition>
-        <isset property="PRODUCT_DIR" />
-      </condition>
-      <else>
-        <fail message="PRODUCT_DIR env var not set?" />
-      </else>
-    </if>
-  </target>
+  <fail message="PRODUCT_DIR env var not set?">
+    <condition>
+      <not>
+        <isset property="PRODUCT_DIR"/>
+      </not>
+    </condition>
+  </fail>
 
   <target name="-post-compile">
     <!-- copy gdbserver to main libs directory if building debug.
       TODO(jrg): for now, Chrome on Android always builds native code
       as Release and java/ant as Debug, which means we always install
       gdbserver.  Resolve this discrepancy, possibly by making this
       Release Official build java/ant as Release. -->
     <if>
       <condition>
         <equals arg1="${build.target}" arg2="debug" />
       </condition>
       <then>
         <echo message="Copying gdbserver to the apk to enable native debugging"/>
         <copy todir="${out.dir}/libs/${target.abi}">
           <path refid="native.libs.gdbserver"/>
         </copy>
       </then>
     </if>
   </target>
 
   <import file="${sdk.dir}/tools/ant/build.xml" />
 
 </project>