title: shrinkResources set to true, but all unused resources (specifically drawables) not getting removed
body: <p>I'm setting shrinkResources to true as follows:</p>
  
  <pre><code>releasepro {
      minifyEnabled true
      shrinkResources true
      proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
      applicationIdSuffix ".pro"
  }
  </code></pre>
  
  <p>But this is removing only a few unused resources. I am aware that gradle does some guessing and leaves resources that is is not sure are unused. Is there a way to remove all unused resources 100% ?</p>
  
  <p>I read about setting the shrinkMode to strict in another thread. Will that help? I could not try it as I could not figure where to set it. Looked for examples and documents but unfortunately could not get to the right page.</p>
  
  <p>Is there a way to ensure 100% removal of unused resources?</p>