docs: Note behavior of PREFER_OFFLINE

Resets developer expectations on the way to deprecation of a parameter
in the Android Speech APIs.

This change was made by hand in the refdoc HTML (cl/303351535);
making the corresponding change to the source code, so the doc
fix won't be reverted with the next DP update.

Bug: 151475334
Test: make ds-docs
Exempt-from-owner-approval: Docs-only change
Change-Id: I053a8e9d9623c394954a118b5e068fc4015b2ba7

core/java/android/speech/RecognizerIntent.java

@@ -413,6 +413,10 @@ public class RecognizerIntent {
      * {@link #ACTION_VOICE_SEARCH_HANDS_FREE}, {@link #ACTION_WEB_SEARCH} to indicate whether to
      * only use an offline speech recognition engine. The default is false, meaning that either
      * network or offline recognition engines may be used.
+     *
+     * <p>Depending on the recognizer implementation, these values may have
+     * no effect.</p>
+     *
      */
     public static final String EXTRA_PREFER_OFFLINE = "android.speech.extra.PREFER_OFFLINE";
 }