Remove some HashMap

sky/engine/tonic/dart_gc_context.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_TONIC_DART_GC_CONTEXT_H_
 #define SKY_ENGINE_TONIC_DART_GC_CONTEXT_H_
 
+#include <unordered_map>
+
 #include "base/macros.h"
 #include "dart/runtime/include/dart_api.h"
-#include "sky/engine/wtf/HashMap.h"
 
 namespace blink {
 
 class DartGCContext {
  public:
   DartGCContext();
   ~DartGCContext();
 
   Dart_WeakReferenceSet AddToSetForRoot(const void* root,
                                         Dart_WeakPersistentHandle handle);
 
  private:
   Dart_WeakReferenceSetBuilder builder_;
-  HashMap<const void*, Dart_WeakReferenceSet> references_;
+  std::unordered_map<const void*, Dart_WeakReferenceSet> references_;
 
   DISALLOW_COPY_AND_ASSIGN(DartGCContext);
 };
 
 }  // namespace blink
 
 #endif  // SKY_ENGINE_TONIC_DART_GC_CONTEXT_H_