Make apk targets remove .class files before compile

build/android/ant/sdk-targets.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="chrome_sdk_overrides" >
   <!--
     Redefinition of targets used by SDK tools.
     Supported version: SDK tools revision 20.
 
     SDK tools do not allow easy way of extending classpaths
     for aidl and javac. This file defines targets which can be used to
     override targets used by tools.
   -->
+  <target name="-pre-compile">
+    <!--
+      Remove all .class files from the output directory. This prevents inclusion of incorrect .class
+      files in the final apk. For example, if a .java file was deleted, the apk should not contain
+      the .class files for that .java from previous builds.
+    -->
+    <delete>
+      <fileset dir="${out.classes.absolute.dir}" includes="**/*.class"/>
+    </delete>
+  </target>
+
   <!--
     Override the -compile target.
     This target requires 'javac.custom.classpath' to be set to reference
     of classpath to be used for javac. Also accepts custom path for
     sources: 'javac.custom.sourcepath'.
   -->
   <target
       name="-compile"
       depends="-build-setup, -pre-build, -code-gen, -pre-compile">
     <do-only-if-manifest-hasCode elseText="hasCode = false. Skipping..." >
@@ skipping 125 matching lines @@
         <!-- Zip aligns the APK -->
         <zipalign-helper
           in.package="${out.unaligned.file}"
           out.package="${out.final.file}" />
         <echo level="info">Release Package: ${out.final.file}</echo>
       </sequential>
     </do-only-if-not-library>
     <record-build-info />
   </target>
 </project>