[blimp] Add support for having multiple tabs

blimp/client/core/contents/navigation_feature.cc

Index: blimp/client/core/contents/navigation_feature.cc
diff --git a/blimp/client/core/contents/navigation_feature.cc b/blimp/client/core/contents/navigation_feature.cc
index 2660441f13c6bacb6cf570ecad2c7ea6d8cd3941..965b9a819f1773f382de3e4881d6d49df0761efa 100644
--- a/blimp/client/core/contents/navigation_feature.cc
+++ b/blimp/client/core/contents/navigation_feature.cc
@@ -94,7 +94,13 @@ void NavigationFeature::ProcessMessage(
   const NavigationMessage& navigation_message = message->navigation();
 
   NavigationFeatureDelegate* delegate = FindDelegate(tab_id);
-  DCHECK(delegate) << "NavigationFeatureDelegate not found for tab " << tab_id;
+  if (!delegate) {
+    VLOG(1) << "NavigationFeatureDelegate not found for " << tab_id
+            << ". Ignoring.";
+    callback.Run(net::OK);
+    return;
+  }
+
   switch (navigation_message.type()) {
     case NavigationMessage::NAVIGATION_STATE_CHANGED: {
       const NavigationStateChangeMessage& details =