[tracing] Add a dump provider to dump process memory totals.

base/trace_event/process_memory_totals_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/process_memory_totals_dump_provider.h"
+
+#include "base/process/process_metrics.h"
+#include "base/trace_event/process_memory_dump.h"
+#include "base/trace_event/process_memory_totals.h"
+
+namespace base {
+namespace trace_event {
+
+// static
+ProcessMemoryTotalsDumpProvider*
+ProcessMemoryTotalsDumpProvider::GetInstance() {
+  return Singleton<
+      ProcessMemoryTotalsDumpProvider,
+      LeakySingletonTraits<ProcessMemoryTotalsDumpProvider>>::get();
+}
+
+ProcessMemoryTotalsDumpProvider::ProcessMemoryTotalsDumpProvider()
+    : process_metrics_(
+          ProcessMetrics::CreateProcessMetrics(GetCurrentProcessHandle())) {
+}
+
+ProcessMemoryTotalsDumpProvider::~ProcessMemoryTotalsDumpProvider() {
+}
+
+// Called at trace dump point time. Creates a snapshot the memory counters for
+// the current process.
+void ProcessMemoryTotalsDumpProvider::DumpInto(ProcessMemoryDump* pmd) {
+  const uint64 rss_bytes = process_metrics_->GetWorkingSetSize();

[dsinclair, 2015/02/18 18:42:30]

So, do the process_metrics_ get updated or are they set at the time when we
create the ProcessMemoryTotalsDumpProvider? If they are set, can we just store
rss_size instead of the whole object?

[Primiano Tucci (use gerrit), 2015/02/18 18:47:59]

process_metrics_ is the (base::) object which is able to retrieve memory
counters for the system (i.e. the same that chrome://memory uses)
For what concerns memory, its only state is the ProcessHandle (i.e. the PID) of
the target process (self). It keeps also other state for CPU measurements (the
last ticks to get the delta) but we never use that part.

At the end, anyways, we have only one instance of ProcessMetrics per chrome
process, which is costing few some extra bytes (~6 PODs), so it shouldn't be a
great deal.

+  pmd->SetProcessTotals(make_scoped_ptr(new ProcessMemoryTotals(rss_bytes)));
+}
+
+}  // namespace trace_event
+}  // namespace base