Add peak memory usage metric

chrome/browser/metrics/metrics_memory_details.h

Index: chrome/browser/metrics/metrics_memory_details.h
diff --git a/chrome/browser/metrics/metrics_memory_details.h b/chrome/browser/metrics/metrics_memory_details.h
index f833afbc82abfd528572eab33b22fb2c3598dbef..9743db6f76e922973ff816bafa669337c35554bb 100644
--- a/chrome/browser/metrics/metrics_memory_details.h
+++ b/chrome/browser/metrics/metrics_memory_details.h
@@ -38,13 +38,29 @@ class MemoryGrowthTracker {
   DISALLOW_COPY_AND_ASSIGN(MemoryGrowthTracker);
 };
 
+// PeakMemoryUsageTracker tracks the peak memory usage.
+class PeakMemoryUsageTracker {
+ public:
+  PeakMemoryUsageTracker();
+
+  // Call with current memory usage. Returns true if the peak has been updated.
+  bool Update(int memory_usage);

[haraken, 2016/12/12 11:41:00]

unsigned long long?

+  int peak() { return peak_; }
+
+ private:
+  int peak_;

[haraken, 2016/12/12 11:41:00]

unsigned long long?

+
+  DISALLOW_COPY_AND_ASSIGN(PeakMemoryUsageTracker);
+};
+
 // Handles asynchronous fetching of memory details and logging histograms about
 // memory use of various processes.
 // Will run the provided callback when finished.
 class MetricsMemoryDetails : public MemoryDetails {
  public:
   MetricsMemoryDetails(const base::Closure& callback,
-                       MemoryGrowthTracker* memory_growth_tracker);
+                       MemoryGrowthTracker* memory_growth_tracker,
+                       PeakMemoryUsageTracker* peak_memory_usage_tracker);
 
   void set_generate_histograms(bool generate_histograms) {
     generate_histograms_ = generate_histograms;
@@ -75,6 +91,11 @@ class MetricsMemoryDetails : public MemoryDetails {
   // If it is null, nothing is tracked.
   MemoryGrowthTracker* memory_growth_tracker_;
 
+  // A pointer to PeakMemoryUsageTracker which is contained in a longer-lived
+  // owner of MetricsMemoryDetails, for example, ChromeMetricsServiceClient.
+  // If it is null, nothing is tracked.
+  PeakMemoryUsageTracker* peak_memory_usage_tracker_;
+
   // A flag indicating if histogram data should be generated. True on default.
   // If false, then only MemoryGrowthTracker gets notified about memory usage.
   bool generate_histograms_;