title: Returning to parent activity's existing instance from another activity
body: <p>I am creating a library project which has chat feature, so user has to register his launch activity as parent in order to perform backstacking(navigating back).
  here is my manifest for sample app..</p>
  
  <pre><code>&lt;activity
              android:name=".MainActivity"
              android:label="@string/app_name"
              android:launchMode="singleTop"&gt;
              &lt;intent-filter&gt;
                  &lt;action android:name="android.intent.action.MAIN" /&gt;
                  &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
              &lt;/intent-filter&gt;
          &lt;/activity&gt;
          &lt;activity
              android:name="com.ak.messages.ChatActivity"
              android:label="@string/app_name"
              android:screenOrientation="sensorPortrait"
              android:parentActivityName=".MainActivity"
              android:theme="@style/AppTheme"
              android:windowSoftInputMode="adjustResize"&gt;
              &lt;meta-data android:name="android.support.PARENT_ACTIVITY"
                  android:value=".MainActivity" /&gt;
          &lt;/activity&gt;
  </code></pre>
  
  <p>and here is how i am trying to navigate back from ChatActivity</p>
  
  <pre><code>   @Override
      public void onBackPressed() {
          Intent intent = NavUtils.getParentActivityIntent(this);
              if(intent!=null){
              intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
                  startActivity(intent);
  
          }
  //      super.onBackPressed();
      }
  </code></pre>
  
  <p>But its always creating a new instance. is there any way to ensure that same MainActivity's Instance gets revoked when user performs back-press? </p>
  
  <blockquote>
    <p>PS: Chat activity is not directly invoked by MainActivity I have
    provided with APIs to launch it.</p>
  </blockquote>
  
  <p>Thank you.</p>