[tracing] Introduce support for userland memory allocators dumps.

base/trace_event/memory_dump_provider.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_dump_provider.h"
+
+#include "base/logging.h"
+
+namespace base {
+namespace trace_event {
+
+MemoryDumpProvider::MemoryDumpProvider()
+    : allocator_attributes_(new MemoryAllocatorDeclaredAttributes()) {
+}
+
+MemoryDumpProvider::~MemoryDumpProvider() {
+}
+
+}  // namespace trace_event
+}  // namespace base