Remove all remaining HashMap and HashSet usages except dart_string_cache

sky/engine/tonic/dart_timer_heap.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_TIMER_HEAP_H_
 #define SKY_ENGINE_TONIC_DART_TIMER_HEAP_H_
 
+#include <unordered_map>
+
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "dart/runtime/include/dart_api.h"
 #include "sky/engine/tonic/dart_persistent_value.h"
-#include "sky/engine/wtf/HashMap.h"
 #include "sky/engine/wtf/OwnPtr.h"
 #include "sky/engine/wtf/PassOwnPtr.h"
 
 namespace blink {
 
 class DartTimerHeap {
  public:
   DartTimerHeap();
   ~DartTimerHeap();
 
   struct Task {
     DartPersistentValue closure;
     base::TimeDelta delay;
     bool repeating = false;
   };
 
   int Add(PassOwnPtr<Task> task);
   void Remove(int id);
 
  private:
   void Schedule(int id, PassOwnPtr<Task> task);
   void Run(int id);
 
   int next_timer_id_;
-  HashMap<int, OwnPtr<Task>> heap_;
+  std::unordered_map<int, OwnPtr<Task>> heap_;
 
   base::WeakPtrFactory<DartTimerHeap> weak_factory_;
 };
 
 }
 
 #endif  // SKY_ENGINE_TONIC_DART_TIMER_HEAP_H_