am cf6a3b91: Update ddms and profiling docs to include sample profiling.

    <li>Click the <strong>Start Method Profiling</strong> button.</li>

    <li>In Android 4.4 and later, choose either trace-based profiling or sample-based profiling

    with a specified sampling interval. For earlier versions of Android, only trace-based profiling

    is available.</li>

    <li>Interact with your application to start the methods that you want to profile.</li>

    <li>Click the <strong>Stop Method Profiling</strong> button. DDMS stops profiling your

  times are only useful in relation to other profile output, so you can see if changes have made

  the code faster or slower relative to a previous profiling run.</p>

  <p>In Android 4.4 and later, you can use sample-based profiling to profile with less runtime

  performance impact. To enable sample profiling, call {@link

  android.os.Debug#startMethodTracingSampling() startMethodTracingSampling()} with a specified

  sampling interval. The system will then gather samples periodically until tracing is stopped

  via {@link android.os.Debug#stopMethodTracing() stopMethodTracing()}.</p>

  <h2 id="copyingfiles">Copying Trace Files to a Host Machine</h2>

  <p>After your application has run and the system has created your trace files

      Traceview logging does not handle threads well, resulting in these two problems:

      <ol>

        <li>If a thread exits during profiling, the thread name is not emitted;</li>

        <li>If a thread exits during profiling, the thread name is not emitted (fixed in Android 5.1

	and later);</li>

        <li>The VM reuses thread IDs. If a thread stops and another starts, they may get the same

        ID.</li>