[tracing] Simplify design of MemoryAllocatorDump

base/trace_event/memory_allocator_attributes.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 BASE_TRACE_EVENT_MEMORY_ALLOCATOR_ATTRIBUTES_H_
-#define BASE_TRACE_EVENT_MEMORY_ALLOCATOR_ATTRIBUTES_H_
-
-#include <string>
-
-#include "base/base_export.h"
-#include "base/containers/hash_tables.h"
-
-namespace base {
-namespace trace_event {
-
-struct BASE_EXPORT MemoryAllocatorDeclaredAttribute {
-  std::string name;
-
-  // Refer to src/tools/perf/unit-info.json for the semantic of the type.
-  std::string type;
-};
-
-using MemoryAllocatorDeclaredAttributes =
-    hash_map<std::string, MemoryAllocatorDeclaredAttribute>;
-
-}  // namespace trace_event
-}  // namespace base
-
-#endif  // BASE_TRACE_EVENT_MEMORY_ALLOCATOR_ATTRIBUTES_H_