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

base/trace_event/process_memory_totals.h

Index: base/trace_event/process_memory_totals.h
diff --git a/base/trace_event/process_memory_totals.h b/base/trace_event/process_memory_totals.h
new file mode 100644
index 0000000000000000000000000000000000000000..b355991f25ddd549e04284691cbe6164d12bef72
--- /dev/null
+++ b/base/trace_event/process_memory_totals.h
@@ -0,0 +1,37 @@
+// 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.
+
+#ifndef BASE_TRACE_EVENT_PROCESS_MEMORY_TOTALS_H_
+#define BASE_TRACE_EVENT_PROCESS_MEMORY_TOTALS_H_
+
+#include "base/base_export.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace base {
+
+class Value;
+
+namespace trace_event {
+
+// Dump provider which collects process-wide memory stats.
+class BASE_EXPORT ProcessMemoryTotals {
+ public:
+  explicit ProcessMemoryTotals(uint64 resident_set_bytes);
+
+  // Called at trace generation time. Will create and return the base::Value
+  // that will be serialized and packed in the trace.
+  scoped_ptr<Value> AsValue() const;

[nduca, 2015/02/18 20:10:52]

Please switch to the the AsValueInto design pattern from cc/. MDM would create
the toplevel trace value builder, then call AsValueinto passing around the value
object. There are eventual performance reasons why that approach is better:
namely, with value construction, the actual operator-new becomes the
[horrifyingly heavy] bottleneck. The builder interface can be changed to not
actually have a value internally and instead push into a pickle, eliminating all
the mallocs.

[Primiano Tucci (use gerrit), 2015/02/19 12:18:12]

Done. thanks for the observation.
Yeah, actually there was no need to reinvent AppendAsTraceFormat as TracedValue
does that for free and keeps the code here more generic.

+
+  uint64 resident_set_bytes() const { return resident_set_bytes_; }
+
+ private:
+  const uint64 resident_set_bytes_;
+
+  DISALLOW_COPY_AND_ASSIGN(ProcessMemoryTotals);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_PROCESS_MEMORY_TOTALS_H_