[tracing] Simplify MemoryDumpProvider interface

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/single_thread_task_runner.h"
-
-namespace base {
-namespace trace_event {
-
-MemoryDumpProvider::MemoryDumpProvider() {
-}
-
-MemoryDumpProvider::MemoryDumpProvider(
-    const scoped_refptr<SingleThreadTaskRunner>& task_runner)
-    : task_runner_(task_runner) {
-}
-
-MemoryDumpProvider::~MemoryDumpProvider() {
-}
-
-void MemoryDumpProvider::DeclareAllocatorAttribute(
-    const std::string& allocator_name,
-    const std::string& attribute_name,
-    const std::string& attribute_type) {
-  allocator_attributes_type_info_.Set(
-      allocator_name, attribute_name, attribute_type);
-}
-
-}  // namespace trace_event
-}  // namespace base