Bug 1399039 - Don't initialize GlobalPageMetadata more than once r=sebastian

MozReview-Commit-ID: 6VqkvDrEc5K

--HG--
extra : rebase_source : 8cb917de8c7605097abaa69caeca0c39bd50ecf5

mobile/android/base/java/org/mozilla/gecko/GlobalPageMetadata.java

@@ -47,6 +47,8 @@ import java.util.Map;
     private final Map<String, GeckoBundle> queuedMetadata =
             Collections.synchronizedMap(new LimitedLinkedHashMap<String, GeckoBundle>());
 
+    private boolean initialized;
+
     public static GlobalPageMetadata getInstance() {
         return instance;
     }
@@ -67,9 +69,15 @@ import java.util.Map;
     private GlobalPageMetadata() {}
 
     public void init() {
+        if (initialized) {
+            return;
+        }
+
         EventDispatcher
                 .getInstance()
                 .registerBackgroundThreadListener(this, GlobalHistory.EVENT_URI_AVAILABLE_IN_HISTORY);
+
+        initialized = true;
     }
 
     public void add(BrowserDB db, ContentProviderClient contentProviderClient, String uri, boolean hasImage, @NonNull String metadataJSON) {