Add more generic support for java targets bundling multiple directories

chrome/android/testshell/javatests/chromium_testshell_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="ChromiumTestShellTest" default="debug" basedir=".">
 
   <description>
     Building ChromiumTestShellTest.apk
   </description>
 
   <import file="../../../../build/android/ant/common.xml"/>
 
   <property name="target.abi" value="${APP_ABI}"/>
   <property-location name="out.dir" location="${PRODUCT_DIR}/chromium_testshell_test"
       check-exists="false"/>
   <property name="resource.absolute.dir" value="${RESOURCE_DIR}"/>
   <property name="gen.absolute.dir" value="${out.dir}/gen"/>
   <property-location name="native.libs.absolute.dir" location="${out.dir}/libs"
       check-exists="false"/>
   <property-location name="asset.absolute.dir" location="${out.dir}/assets"
       check-exists="false"/>
   <!-- Set the output directory for the final apk to the ${apks.dir}. -->
   <property-location name="out.final.file"
       location="${apks.dir}/${ant.project.name}-debug.apk"
       check-exists="false"/>
   <property name="generate.test.jar" value="true"/>
 
+  <path id="javac.custom.sourcepath">
+    <filelist files="${ADDITIONAL_SRC_DIRS}"/>
+    <filelist files="${GENERATED_SRC_DIRS}"/>
+  </path>
+
   <path id="out.dex.jar.input.ref">
     <filelist files="${INPUT_JARS_PATHS}"/>
   </path>
 
-  <path id="javac.custom.sourcepath">
-    <pathelement location="../../javatests/src" />
-  </path>
-
   <!-- Classpath for javac -->
   <path id="javac.custom.classpath">
     <path refid="out.dex.jar.input.ref"/>
   </path>
 
   <import file="../../../../build/android/ant/sdk-targets.xml"/>
   <import file="${sdk.dir}/tools/ant/build.xml" />
 </project>