Allow multiple dart <script> tags in .sky files

sky/engine/core/script/dart_loader.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_loader.h"
 
 #include "base/callback.h"
 #include "mojo/common/data_pipe_drainer.h"
 #include "sky/engine/core/script/dart_dependency_catcher.h"
@@ skipping 189 matching lines @@
     CHECK(WTF::isMainThread());
     return DOMDartState::Current()->loader().Source(library, url);
   }
   DCHECK(false);
   return Dart_NewApiError("Unknown library tag.");
 }
 
 void DartLoader::WaitForDependencies(
     const HashSet<DartDependency*>& dependencies,
     const base::Closure& callback) {
+  if (dependencies.isEmpty())
+    return callback.Run();
   dependency_watchers_.add(
       adoptPtr(new DependencyWatcher(dependencies, callback)));
 }
 
 Dart_Handle DartLoader::Import(Dart_Handle library, Dart_Handle url) {
   KURL parsed_url(ParsedURLString, StringFromDart(url));
   const auto& result = pending_libraries_.add(parsed_url.string(), nullptr);
   if (result.isNewEntry) {
     OwnPtr<Job> job = adoptPtr(new ImportJob(this, parsed_url));
     result.storedValue->value = job.get();
@@ skipping 53 matching lines @@
 
   WatcherSignaler watcher_signaler(*this, job);
 
   LOG(ERROR) << "Library Load failed: " << job->url().string().utf8().data();
   // TODO(eseidel): Call Dart_LibraryHandleError in the SourceJob case?
 
   jobs_.remove(job);
 }
 
 }  // namespace blink