[tracing] Dump child processes' memory metrics in browser

components/tracing/process_metrics_memory_dump_manager.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 "components/tracing/process_metrics_memory_dump_manager.h"
+
+#include "base/trace_event/memory_dump_manager.h"
+#include "base/trace_event/memory_dump_provider.h"
+#include "components/tracing/process_metrics_memory_dump_provider.h"
+
+namespace tracing {
+
+// static
+ProcessMetricsMemoryDumpManager*
+ProcessMetricsMemoryDumpManager::GetInstance() {
+  return base::Singleton<
+      ProcessMetricsMemoryDumpManager,
+      base::LeakySingletonTraits<ProcessMetricsMemoryDumpManager>>::get();
+}
+
+void ProcessMetricsMemoryDumpManager::RegisterForProcess(
+    base::ProcessHandle process) {
+#if !defined(OS_LINUX)
+  // Register dump provider for child processes only on linux.
+  if (process != base::kNullProcessHandle)

[Primiano Tucci (use gerrit), 2015/11/17 10:44:12]

not sure I understand this.
This is saying: on Non-Linux, if you try to RegisterForProcess(some child pid)
silently turn this into a noop?
Why is this needed? Can we remove lines 23-27 completely?

[ssid, 2015/11/17 11:13:07]

If I do not add this here then I would have to change the tracing controller to
have a if defined(OS_LINUX) then register. I thought it is better to have this
ifdefs in one place.

[ssid, 2015/11/17 13:55:06]

Done.

+    return;
+#endif
+#if !defined(OS_NACL)
+  scoped_ptr<ProcessMetricsMemoryDumpProvider> metrics_provider(
+      new ProcessMetricsMemoryDumpProvider(process));
+  base::trace_event::MemoryDumpProvider::Options options(process);
+  base::trace_event::MemoryDumpManager::GetInstance()->RegisterDumpProvider(
+      metrics_provider.get(), "ProcessMemoryMetrics", nullptr, options);
+  process_metrics_providers_map_.insert(process, metrics_provider.Pass());
+#endif
+}
+
+void ProcessMetricsMemoryDumpManager::UnregisterForProcess(
+    base::ProcessHandle process) {
+#if !defined(OS_NACL)
+  scoped_ptr<ProcessMetricsMemoryDumpProvider> provider =
+      process_metrics_providers_map_.take_and_erase(process);
+  DCHECK(provider);
+  base::trace_event::MemoryDumpManager::GetInstance()
+      ->UnregisterAndDeleteDumpProviderAsync(provider.Pass());
+#endif  // defined(OS_LINUX)
+}
+
+ProcessMetricsMemoryDumpManager::ProcessMetricsMemoryDumpManager() {}
+ProcessMetricsMemoryDumpManager::~ProcessMetricsMemoryDumpManager() {}
+
+}  // namespace tracing