Don't crash when main.dart is a 404.

sky/engine/core/script/dart_controller.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
 #include "sky/engine/core/script/dart_controller.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 101 matching lines @@
 
 void DartController::DidLoadMainLibrary(KURL url) {
   DCHECK(Dart_CurrentIsolate() == dart_state()->isolate());
   DartApiScope dart_api_scope;
 
   if (LogIfError(Dart_FinalizeLoading(true)))
     return;
 
   Dart_Handle library = Dart_LookupLibrary(
       StringToDart(dart_state(), url.string()));
-  CHECK(!LogIfError(library));
+  // TODO(eseidel): We need to load a 404 page instead!
+  if (LogIfError(library))
+    return;
   DartInvokeAppField(library, ToDart("main"), 0, nullptr);
 }
 
 void DartController::LoadMainLibrary(const KURL& url, mojo::URLResponsePtr response) {
   DartLoader& loader = dart_state()->loader();
   DartDependencyCatcher dependency_catcher(loader);
   loader.LoadLibrary(url, response.Pass());
   loader.WaitForDependencies(dependency_catcher.dependencies(),
                              base::Bind(&DartController::DidLoadMainLibrary, weak_factory_.GetWeakPtr(), url));
 }
@@ skipping 254 matching lines @@
                         nullptr,  // Isolate interrupt callback.
                         UnhandledExceptionCallback, IsolateShutdownCallback,
                         // File IO callbacks.
                         nullptr, nullptr, nullptr, nullptr, nullptr));
   // Wait for load port- ensures handle watcher and service isolates are
   // running.
   Dart_ServiceWaitForLoadPort();
 }
 
 } // namespace blink