[tracing] Introduce support for userland memory allocators dumps.

base/trace_event/memory_allocator_attributes.cc

+// 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.
+
+#include "base/trace_event/memory_allocator_attributes.h"
+
+namespace base {
+namespace trace_event {
+
+MemoryAllocatorDeclaredAttributes::MemoryAllocatorDeclaredAttributes() {
+}
+
+MemoryAllocatorDeclaredAttributes::~MemoryAllocatorDeclaredAttributes() {
+}
+
+void MemoryAllocatorDeclaredAttributes::Add(
+    const MemoryAllocatorDeclaredAttribute& attr) {
+  DCHECK_EQ(0u, attributes_.count(attr.name));
+  attributes_[attr.name] = attr;
+}
+
+const MemoryAllocatorDeclaredAttribute* MemoryAllocatorDeclaredAttributes::Get(
+    const std::string& name) const {
+  auto it = attributes_.find(name);
+  return it == attributes_.end() ? nullptr : &(it->second);
+}
+
+}  // namespace trace_event
+}  // namespace base