[tracing] Introduce support for userland memory allocators dumps.

base/trace_event/memory_dump_provider.cc

Index: base/trace_event/memory_dump_provider.cc
diff --git a/base/trace_event/memory_dump_provider.cc b/base/trace_event/memory_dump_provider.cc
new file mode 100644
index 0000000000000000000000000000000000000000..9518461dcf77906c8502d187410f53ba23755db0
--- /dev/null
+++ b/base/trace_event/memory_dump_provider.cc
@@ -0,0 +1,27 @@
+// 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() {
+}
+
+MemoryDumpProvider::~MemoryDumpProvider() {
+}
+
+void MemoryDumpProvider::DeclareAllocatorAttribute(
+    const MemoryAllocatorDeclaredAttribute& attr) {
+  DCHECK_EQ(0u, allocator_attributes_.count(attr.name))
+      << "Allocator attribute " << attr.name << " already declared for dumper "
+      << GetFriendlyName();
+  allocator_attributes_[attr.name] = attr;
+}
+
+}  // namespace trace_event
+}  // namespace base