Bug 857335 - Add EventDispatcher warnings about events with no listeners. r=mfinkle r=kats

mobile/android/base/util/EventDispatcher.java

@@ -27,7 +27,7 @@ public final class EventDispatcher {
                 // Otherwise we could end up throwing a ConcurrentModificationException.
                 listeners = new CopyOnWriteArrayList<GeckoEventListener>();
             } else if (listeners.contains(listener)) {
-                Log.w(LOGTAG, "EventListener already registered for event \"" + event + "\"",
+                Log.w(LOGTAG, "EventListener already registered for event '" + event + "'",
                       new IllegalArgumentException());
             }
             listeners.add(listener);
@@ -39,9 +39,13 @@ public final class EventDispatcher {
         synchronized (mEventListeners) {
             CopyOnWriteArrayList<GeckoEventListener> listeners = mEventListeners.get(event);
             if (listeners == null) {
+                Log.w(LOGTAG, "unregisterEventListener: event '" + event + "' has no listeners");
                 return;
             }
-            listeners.remove(listener);
+            if (!listeners.remove(listener)) {
+                Log.w(LOGTAG, "unregisterEventListener: tried to remove an unregistered listener " +
+                              "for event '" + event + "'");
+            }
             if (listeners.size() == 0) {
                 mEventListeners.remove(event);
             }
@@ -55,19 +59,26 @@ public final class EventDispatcher {
         //   ...
         try {
             JSONObject json = new JSONObject(message);
-            if (json.has("gecko")) {
-                json = json.getJSONObject("gecko");
-                Log.w(LOGTAG, "The 'gecko' property of the sendMessageToJava parameter is deprecated; message of type " + json.getString("type"));
+            JSONObject gecko = json.has("gecko") ? json.getJSONObject("gecko") : null;
+            if (gecko != null) {
+                json = gecko;
             }
+
             String type = json.getString("type");
 
+            if (gecko != null) {
+                Log.w(LOGTAG, "Message '" + type + "' has deprecated 'gecko' property!");
+            }
+
             CopyOnWriteArrayList<GeckoEventListener> listeners;
             synchronized (mEventListeners) {
                 listeners = mEventListeners.get(type);
             }
 
-            if (listeners == null)
+            if (listeners == null || listeners.size() == 0) {
+                Log.d(LOGTAG, "dispatchEvent: no listeners registered for event '" + type + "'");
                 return "";
+            }
 
             String response = null;