Factor DartLibraryProvider out of DartLoader

sky/engine/core/script/dart_dependency_catcher.h

-// 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.
-
-#ifndef SKY_ENGINE_CORE_SCRIPT_DEPENDENCY_CATCHER_H_
-#define SKY_ENGINE_CORE_SCRIPT_DEPENDENCY_CATCHER_H_
-
-#include "base/macros.h"
-#include "sky/engine/wtf/HashSet.h"
-
-namespace blink {
-class DartLoader;
-
-// A base class to represent a dependency.
-class DartDependency {
-};
-
-// To catch the dependencies for a library, put a DartDependencyCatcher on the
-// stack during the call to Dart_LoadLibrary.
-class DartDependencyCatcher {
- public:
-  explicit DartDependencyCatcher(DartLoader& loader);
-  ~DartDependencyCatcher();
-
-  void AddDependency(DartDependency* dependency);
-  const HashSet<DartDependency*>& dependencies() const { return dependencies_; }
-
- private:
-  DartLoader& loader_;
-  HashSet<DartDependency*> dependencies_;
-
-  DISALLOW_COPY_AND_ASSIGN(DartDependencyCatcher);
-};
-
-}  // namespace blink
-
-#endif  // SKY_ENGINE_CORE_SCRIPT_DEPENDENCY_CATCHER_H_