title: Proguard fails with firebase FCM
body: <p>HI I am using Google Firebase Cloud Messaging in my application just now.  </p>
  
  <p>Prior to using FCM I was able to generate release apk with <code>buildToolsVersion 23.0.2</code></p>
  
  <p>as I have updated <code>buildToolsVersion 25.0.2</code> and added few firebase dependencies, I am suddenly getting exception:</p>
  
  <pre><code>Warning: there were 1 unresolved references to library class members.
           You probably need to update the library versions.
           (http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedlibraryclassmember)
  Warning: Exception while processing task java.io.IOException: Please correct the above warnings first.
  :app:transformClassesAndResourcesWithProguardForRelease FAILED
  :app:transformClassesAndResourcesWithProguardForRelease (Thread[Task worker Thread 6,5,main]) completed. Took 4.354 secs.
  
  FAILURE: Build failed with an exception.
  
  * What went wrong:
  Execution failed for task ':app:transformClassesAndResourcesWithProguardForRelease'.
  &gt; Job failed, see logs for details
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --debug option to get more log output.
  
  BUILD FAILED
  </code></pre>
  
  <p>Is there anything I need add to <code>proguard.txt</code> for firebase?</p>
  
  <p>My Firebase dependencies are as follows:</p>
  
  <pre><code>compile 'com.google.firebase:firebase-core:10.0.1'
  compile 'com.google.firebase:firebase-messaging:10.0.1'
  </code></pre>
  
  <p>Also I am using <strong>Custom Parse SDK</strong> reference from here <a href="https://github.com/ParsePlatform/Parse-SDK-Android/tree/master/Parse" rel="nofollow noreferrer">https://github.com/ParsePlatform/Parse-SDK-Android/tree/master/Parse</a>, I am adding parse sdk as <strong>external project</strong> with little modification in src code according to my needs.</p>