Replace uses of hash_map in //base

base/memory/shared_memory_tracker.h

 // Copyright 2017 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 BASE_MEMORY_SHARED_MEMORY_TRACKER_H_
 #define BASE_MEMORY_SHARED_MEMORY_TRACKER_H_
 
+#include <unordered_map>
+
 #include "base/memory/shared_memory.h"
 #include "base/synchronization/lock.h"
 #include "base/trace_event/memory_dump_provider.h"
 
 namespace base {
 
 namespace trace_event {
 class ProcessMemoryDump;
 }
 
@@ skipping 29 matching lines @@
   // Used to lock when |usages_| is modified or read.
   Lock usages_lock_;
   std::unordered_map<const SharedMemory*, Usage> usages_;
 
   DISALLOW_COPY_AND_ASSIGN(SharedMemoryTracker);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_TRACKER_H_