Fix the gdb path for NDK-r8b.

build/android/ant/common.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_common_defines">
   <!-- Common build properties for Chrome for android. -->
 
   <!--
@@ skipping 35 matching lines @@
     <attribute name="name"/>
     <attribute name="location"/>
     <attribute name="check-exists" default="true"/>
     <sequential>
       <property name="@{name}" location="@{location}"/>
       <check-property-value property="@{name}"/>
       <fail message="Location specified for @{name} : @{location} does not exist.">
         <condition>
           <and>
             <equals arg1="@{check-exists}" arg2="true"/>
-            <not><available type="dir" file="@{location}"/></not>
+            <not><available file="@{location}"/></not>
           </and>
         </condition>
       </fail>
     </sequential>
   </macrodef>
 
   <!-- A safe setter for property values -->
   <macrodef name="property-value">
     <attribute name="name"/>
     <attribute name="value"/>
     <sequential>
       <property name="@{name}" value="@{value}"/>
       <check-property-value property="@{name}"/>
     </sequential>
   </macrodef>
 
   <!-- Common environment properties. -->
   <property-location name="sdk.dir" location="${ANDROID_SDK_ROOT}"/>
   <property-value name="target" value="android-${ANDROID_SDK_VERSION}"/>
   <property name="source.dir" location="src"/>
-  <property-location name="toolchain.dir" location="${ANDROID_TOOLCHAIN}"/>
+  <property-location name="android.gdbserver" location="${ANDROID_GDBSERVER}"/>
 </project>