Allow EmbedRoot to be called multiple times.

mojo/services/view_manager/test_change_tracker.cc

Index: mojo/services/view_manager/test_change_tracker.cc
diff --git a/mojo/services/view_manager/test_change_tracker.cc b/mojo/services/view_manager/test_change_tracker.cc
index 827a77d41496421ca59bc7a0b6134e32486c6b29..eba216b91a08610b4487419a97fb59ad14c568ba 100644
--- a/mojo/services/view_manager/test_change_tracker.cc
+++ b/mojo/services/view_manager/test_change_tracker.cc
@@ -80,6 +80,8 @@ std::string ChangeToDescription1(const Change& change) {
           "InputEvent view=%s event_action=%d",
           NodeIdToString(change.view_id).c_str(),
           change.event_action);
+    case CHANGE_TYPE_EMBED_ROOT:
+      return base::StringPrintf("EmbedRoot url=%s", change.embed_url.data());
   }
   return std::string();
 }
@@ -223,6 +225,13 @@ void TestChangeTracker::OnViewInputEvent(Id view_id, EventPtr event) {
   AddChange(change);
 }
 
+void TestChangeTracker::OnEmbedRoot(const String& url) {
+  Change change;
+  change.type = CHANGE_TYPE_EMBED_ROOT;
+  change.embed_url = url;
+  AddChange(change);
+}
+
 void TestChangeTracker::AddChange(const Change& change) {
   changes_.push_back(change);
   if (delegate_)