title: Calling finish() does not clear memory references to Activity
body: <p>In a simplified version of my app, I have two activities, A and B.  Actvity A starts B, and after some work B calls finish().  Using the Memory Analyzer Tool on most devices (Galaxy Nexus running 4.2, Droid 4 running 4.0.4, and Droid 2 running 2.3.4) shows no trace of activity B, which is what I expected.</p>
  
  <p>But on Samsung S3 running 4.1.1, MAT shows activity B objects still around, due to paths to the following GC roots (weak/soft references excluded):</p>
  
  <pre><code>Class Name                                                        | Shallow Heap | Retained Heap
  -------------------------------------------------------------------------------------------------
  com.myCo.myApp.ActivityB  @ 0x42720818                            |          264 |         3,280
  |- &lt;Java Local&gt; java.lang.Thread @ 0x4271cf60  Thread-21941 Thread|           80 |        52,264
  |- mOuterContext android.app.ContextImpl @ 0x426adf68             |          104 |           784
      |  '- mContext android.media.AudioManager @ 0x428e49a0        |           48 |           152
  -------------------------------------------------------------------------------------------------
  </code></pre>
  
  <p>Every time I start and stop activity B, MAT shows another instance of activity B's memory footprint.  And the more I open/close activity B, the bigger the memory footprint reported in logcat.  Forcing a GC through MAT does not remove the references to activity B memory.</p>
  
  <p>I have three questions.</p>
  
  <ol>
  <li><p>Why is the memory/GC behavior different across the different devices?</p></li>
  <li><p>On S3, will the OS eventually come back and GC the stranded activity B objects (in other words, should I not worry about it because Android will clean it up before a crash)?</p></li>
  <li><p>If not, where do the Thread and AudioManager references come from, and how would I clear them?</p></li>
  </ol>
  
  <p>Thanks to any experienced "leak hunters" out there!</p>