Update Android build to API level 17 and SDK Tools version 21

build/android/ant/chromium-apk.xml

 <!--
   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 default="error">
   <property name="ant.project.name" value="${APK_NAME}"/>
   <!--
     Gyp will pass CONFIGURATION_NAME as the target for ant to build. These targets will call the
     appropriate sdk tools target.
@@ skipping 23 matching lines @@
   <!--
     Include additional resource folders in the apk, e.g. content/.../res.  We
     list the res folders in project.library.res.folder.path and the
     corresponding java packages in project.library.packages, which must be
     semicolon-delimited while ADDITIONAL_RES_PACKAGES is space-delimited, hence
     the javascript task.
   -->
   <path id="project.library.res.folder.path">
     <filelist files="${ADDITIONAL_RES_DIRS}"/>
   </path>
+  <path id="project.library.bin.r.file.path">
+    <filelist files="${ADDITIONAL_R_TEXT_FILES}"/>
+  </path>
   <script language="javascript">
     var before = project.getProperty("ADDITIONAL_RES_PACKAGES");
     project.setProperty("project.library.packages", before.replaceAll(" ", ";"));
   </script>
 
   <property-value name="target.abi" value="${APP_ABI}"/>
   <property name="resource.absolute.dir" value="${RESOURCE_DIR}"/>
   <property-value name="gen.absolute.dir" value="${out.dir}/gen"/>
   <property-location name="native.libs.absolute.dir" location="${out.dir}/libs"
       check-exists="false"/>
@@ skipping 28 matching lines @@
   </path>
 
   <path id="out.dex.jar.input.ref">
     <path refid="javac.custom.classpath"/>
   </path>
 
   <import file="sdk-targets.xml"/>
   <import file="${sdk.dir}/tools/ant/build.xml"/>
 </project>