[tracing] Introduce support for userland memory allocators dumps.

base/trace_event/memory_allocator_attributes.h

Index: base/trace_event/memory_allocator_attributes.h
diff --git a/base/trace_event/memory_allocator_attributes.h b/base/trace_event/memory_allocator_attributes.h
new file mode 100644
index 0000000000000000000000000000000000000000..0d0bc35a5a008c36d5e08a17f2467a30c1dd08cc
--- /dev/null
+++ b/base/trace_event/memory_allocator_attributes.h
@@ -0,0 +1,43 @@
+// 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"
+#include "base/memory/ref_counted.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;
+};
+
+class BASE_EXPORT MemoryAllocatorDeclaredAttributes
+    : public RefCounted<MemoryAllocatorDeclaredAttributes> {
+ public:
+  MemoryAllocatorDeclaredAttributes();
+
+  void Add(const MemoryAllocatorDeclaredAttribute& attr);
+  const MemoryAllocatorDeclaredAttribute* Get(const std::string& name) const;
+
+ private:
+  friend class RefCounted<MemoryAllocatorDeclaredAttributes>;
+
+  ~MemoryAllocatorDeclaredAttributes();
+
+  hash_map<std::string, MemoryAllocatorDeclaredAttribute> attributes_;
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_MEMORY_ALLOCATOR_ATTRIBUTES_H_