Bug 1322586 - 1. Add "always listen" option for GeckoViewHandler; r=esawin

It would be nice to reuse GeckoViewHandler for delegates too (e.g. for
the new PermissionDelegate), but delegates need to always listen to
their events. This patch adds an "always listen" option for
GeckoViewHandler that still keeps track of the current listener/delegate
instance, but registers for all events at initialization rather than
only when there is a listener.

MozReview-Commit-ID: JtskpZMy9T4

--HG--
extra : rebase_source : 99170bc0b19d605dde4dbf08690bb31d310ed113

mobile/android/geckoview/src/main/java/org/mozilla/gecko/GeckoViewHandler.java

@@ -20,13 +20,25 @@ import android.util.Log;
     private static final boolean DEBUG = false;
 
     private Listener mListener;
+    private final boolean mAlwaysListen;
     private final String mModuleName;
     private final String[] mEvents;
 
+
     GeckoViewHandler(final String module, final GeckoView view,
                      final String[] events) {
+        this(module, view, events, /* alwaysListen */ false);
+    }
+
+    GeckoViewHandler(final String module, final GeckoView view,
+                     final String[] events, final boolean alwaysListen) {
+        mAlwaysListen = alwaysListen;
         mModuleName = module;
         mEvents = events;
+
+        if (alwaysListen) {
+            register(view.getEventDispatcher());
+        }
     }
 
     public Listener getListener() {
@@ -35,20 +47,29 @@ import android.util.Log;
 
     public void setListener(final Listener listener, final GeckoView view) {
         final EventDispatcher eventDispatcher = view.getEventDispatcher();
+        if (mListener == listener) {
+            return;
+        }
 
-        if (mListener != null && mListener != listener) {
+        if (!mAlwaysListen && mListener != null) {
+            unregister(eventDispatcher);
+        }
+
+        mListener = listener;
+
+        if (!mAlwaysListen && mListener != null) {
+            register(eventDispatcher);
+        }
+    }
+
+    private void unregister(final EventDispatcher eventDispatcher) {
         final GeckoBundle msg = new GeckoBundle(1);
         msg.putString("module", mModuleName);
         eventDispatcher.dispatch("GeckoView:Unregister", msg);
         eventDispatcher.unregisterUiThreadListener(this, mEvents);
     }
 
-        mListener = listener;
-
-        if (mListener == null) {
-            return;
-        }
-
+    private void register(final EventDispatcher eventDispatcher) {
         final GeckoBundle msg = new GeckoBundle(1);
         msg.putString("module", mModuleName);
         eventDispatcher.dispatch("GeckoView:Register", msg);