Return unique_ptrs from base::ProcessMetrics.

chrome/browser/performance_monitor/performance_monitor.h

Index: chrome/browser/performance_monitor/performance_monitor.h
diff --git a/chrome/browser/performance_monitor/performance_monitor.h b/chrome/browser/performance_monitor/performance_monitor.h
index 24c7c1e4b661de5b555f0b183c9db6bafc8178f2..25312c03510fae743d5f134e40b56ac09c2d4cb0 100644
--- a/chrome/browser/performance_monitor/performance_monitor.h
+++ b/chrome/browser/performance_monitor/performance_monitor.h
@@ -9,22 +9,20 @@
 #include <memory>
 #include <vector>
 
+#include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/process/process_handle.h"
 #include "base/timer/timer.h"
 #include "chrome/browser/performance_monitor/process_metrics_history.h"
 
-namespace base {
-template <typename Type>
-struct DefaultSingletonTraits;
-}  // namespace base
-
 namespace content {
 struct ChildProcessData;
 }
 
 namespace performance_monitor {
 
+class ProcessMetricsHistory;
+
 // PerformanceMonitor is a tool which periodically monitors performance metrics
 // for histogram logging and possibly taking action upon noticing serious
 // performance degradation.
@@ -38,12 +36,13 @@ class PerformanceMonitor {
   void StartGatherCycle();
 
  private:
-  typedef std::map<base::ProcessHandle, ProcessMetricsHistory> MetricsMap;
+  friend struct base::DefaultLazyInstanceTraits<PerformanceMonitor>;
 
-  friend struct base::DefaultSingletonTraits<PerformanceMonitor>;
+  using MetricsMap =
+      std::map<base::ProcessHandle, std::unique_ptr<ProcessMetricsHistory>>;
 
   PerformanceMonitor();
-  virtual ~PerformanceMonitor();
+  ~PerformanceMonitor();
 
   // Perform any collections that are done on a timed basis.
   void DoTimedCollections();