Add Geocorder.isImplemented()

The Geocorder interface is not part of the Android core.  It
requires a backend service which may or may not be available
on a device.  The new isImplemented static method allows
apps to discover whether the Geocorder is in fact available
on the device.

Change-Id: I2b5cf7bcc9cce4766bcbb156e91edf34b01f9296

location/java/android/location/Geocoder.java

@@ -40,7 +40,9 @@ import java.util.List;
  *
  * The Geocoder class requires a backend service that is not included in
  * the core android framework.  The Geocoder query methods will return an
- * empty list if there no backend service in the platform.
+ * empty list if there no backend service in the platform.  Use the
+ * isImplemented() method to determine whether a Geocoder implementation
+ * exists.
  */
 public final class Geocoder {
     private static final String TAG = "Geocoder";
@@ -48,6 +50,23 @@ public final class Geocoder {
     private GeocoderParams mParams;
     private ILocationManager mService;
 
+    /**
+     * Returns true if the Geocoder methods getFromLocation and
+     * getFromLocationName are implemented.  Lack of network
+     * connectivity may still cause these methods to return null or
+     * empty lists.
+     */
+    public static Boolean isImplemented() {
+        IBinder b = ServiceManager.getService(Context.LOCATION_SERVICE);
+        ILocationManager lm = ILocationManager.Stub.asInterface(b);
+        try {
+            return lm.geocoderIsImplemented();
+        } catch (RemoteException e) {
+            Log.e(TAG, "isImplemented: got RemoteException", e);
+            return false;
+        }
+    }
+
     /**
      * Constructs a Geocoder whose responses will be localized for the
      * given Locale.