Emit an error log line when attempting to connect to an app at an invalid URL.

mojo/application_manager/application_manager.cc

Index: mojo/application_manager/application_manager.cc
diff --git a/mojo/application_manager/application_manager.cc b/mojo/application_manager/application_manager.cc
index 75ef7a76694b24773a65b38e644d83bd901d1ce9..4d1037a6e0265deaafd99b0272a63c323766b208 100644
--- a/mojo/application_manager/application_manager.cc
+++ b/mojo/application_manager/application_manager.cc
@@ -100,8 +100,12 @@ class ApplicationManager::ShellImpl : public InterfaceImpl<Shell> {
       InterfaceRequest<ServiceProvider> in_service_provider) override {
     ServiceProviderPtr out_service_provider;
     out_service_provider.Bind(in_service_provider.PassMessagePipe());
-    manager_->ConnectToApplication(
-        app_url.To<GURL>(), url_, out_service_provider.Pass());
+    GURL app_gurl(app_url);
+    if (!app_gurl.is_valid()) {
+      LOG(ERROR) << "Error: invalid URL: " << app_url;
+      return;
+    }
+    manager_->ConnectToApplication(app_gurl, url_, out_service_provider.Pass());
   }
 
   const GURL& url() const { return url_; }
@@ -175,6 +179,7 @@ void ApplicationManager::ConnectToApplication(
     const GURL& url,
     const GURL& requestor_url,
     ServiceProviderPtr service_provider) {
+  DCHECK(url.is_valid());
   URLToShellImplMap::const_iterator shell_it = url_to_shell_impl_.find(url);
   if (shell_it != url_to_shell_impl_.end()) {
     ConnectToClient(