Suggest smart actions in ExtServices

By using text textclassifier API, we classify entities like
email, phone, address in the notification and suggest the corresponding
actions.

Test: Manual test for now. Sideload GoogleExtServices. Write a sample app
to generate notification with phone number / address, etc, and finally
observe the smart actions.

BUG: 110527159

Change-Id: I02740cb07fa25a588d9e864990f95332d6830f12

core/java/android/app/Notification.java

@@ -202,6 +202,11 @@ public class Notification implements Parcelable
      */
     private static final int MAX_REPLY_HISTORY = 5;
 
+    /**
+     * Maximum numbers of action buttons in a notification.
+     * @hide
+     */
+    public static final int MAX_ACTION_BUTTONS = 3;
 
     /**
      * If the notification contained an unsent draft for a RemoteInput when the user clicked on it,
@@ -3151,8 +3156,6 @@ public class Notification implements Parcelable
         public static final String EXTRA_REBUILD_HEADS_UP_CONTENT_VIEW_ACTION_COUNT
                 = "android.rebuild.hudViewActionCount";
 
-        private static final int MAX_ACTION_BUTTONS = 3;
-
         private static final boolean USE_ONLY_TITLE_IN_LOW_PRIORITY_SUMMARY =
                 SystemProperties.getBoolean("notifications.only_title", true);
 
@@ -7162,8 +7165,8 @@ public class Notification implements Parcelable
         }
 
         public static final class Message {
-
-            static final String KEY_TEXT = "text";
+            /** @hide */
+            public static final String KEY_TEXT = "text";
             static final String KEY_TIMESTAMP = "time";
             static final String KEY_SENDER = "sender";
             static final String KEY_SENDER_PERSON = "sender_person";