Add Startup.TimeSinceLastStartup histogram.

components/startup_metric_utils/browser/startup_metric_utils.cc

Index: components/startup_metric_utils/browser/startup_metric_utils.cc
diff --git a/components/startup_metric_utils/browser/startup_metric_utils.cc b/components/startup_metric_utils/browser/startup_metric_utils.cc
index 5bc42d09e42c99d294ad3bd0b6dcaabda0a259c1..6b43e1673301f980c2637faf18d4a74f1a87b793 100644
--- a/components/startup_metric_utils/browser/startup_metric_utils.cc
+++ b/components/startup_metric_utils/browser/startup_metric_utils.cc
@@ -11,6 +11,9 @@
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/prefs/pref_registry_simple.h"
+#include "base/prefs/pref_service.h"
+#include "base/process/process_info.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/sys_info.h"
 #include "base/threading/platform_thread.h"
@@ -27,6 +30,9 @@ namespace startup_metric_utils {
 
 namespace {
 
+const char kLastStartupTimestampPref[] =
+    "startup_metric.last_startup_timestamp";
+
 // Mark as volatile to defensively make sure usage is thread-safe.
 // Note that at the time of this writing, access is only on the UI thread.
 volatile bool g_non_browser_ui_displayed = false;
@@ -96,6 +102,9 @@ typedef NTSTATUS (WINAPI *NtQuerySystemInformationPtr)(
     SYSTEM_INFORMATION_CLASS, PVOID, ULONG, PULONG);
 #endif  // defined(OS_WIN)
 
+#define UMA_HISTOGRAM_TIME_IN_MINUTES_MONTH_RANGE(name, sample) \
+  UMA_HISTOGRAM_CUSTOM_COUNTS(name, sample, 1,                  \
+                              base::TimeDelta::FromDays(30).InMinutes(), 100)

[Alexei Svitkine (slow), 2016/01/05 20:21:14]

Do you need 100 buckets? I think 50 should be sufficient.

You can look at the data for Variations.SeedFreshness to see the bucket ranges
there to see if that would be sufficient.

[fdoray, 2016/01/05 20:36:14]

Done. I agree that 50 buckets is enough.

 
 // Helper macro for splitting out an UMA histogram based on cold or warm start.
 // |type| is the histogram type, and corresponds to an UMA macro like
@@ -374,6 +383,11 @@ bool GetHardFaultCountForCurrentProcess(uint32_t* hard_fault_count) {
 }
 #endif  // defined(OS_WIN)
 
+void RegisterPrefs(PrefRegistrySimple* registry) {
+  DCHECK(registry);
+  registry->RegisterInt64Pref(kLastStartupTimestampPref, 0);
+}
+
 bool WasNonBrowserUIDisplayed() {
   return g_non_browser_ui_displayed;
 }
@@ -469,6 +483,32 @@ void RecordBrowserMainMessageLoopStart(const base::TimeTicks& ticks,
   }
 }
 
+void RecordTimeSinceLastStartup(PrefService* pref_service) {
+  DCHECK(pref_service);
+
+  // Get the timestamp of the current startup.
+  const base::Time process_start_time =
+      base::CurrentProcessInfo::CreationTime();
+
+  // Get the timestamp of the last startup from |pref_service|.
+  const int64_t last_startup_timestamp_internal =
+      pref_service->GetInt64(kLastStartupTimestampPref);
+  if (last_startup_timestamp_internal != 0) {
+    // Log the Startup.TimeSinceLastStartup histogram.
+    const base::Time last_startup_timestamp =
+        base::Time::FromInternalValue(last_startup_timestamp_internal);
+    const base::TimeDelta time_since_last_startup =
+        process_start_time - last_startup_timestamp;

[Alexei Svitkine (slow), 2016/01/05 20:21:14]

In certain cases, you may get a negative value here - e.g. if system clock was
changed.

For UMA, this would result in going into the underflow bucket which is also the
0 bucket. Perhaps you don't want those samples there? Otherwise you'd be
conflating these two cases (0 minutes vs. clock skew).

[fdoray, 2016/01/05 20:36:14]

Done. We cannot conclude anything from negative values, so I changed the code to
ignore them.

+    UMA_HISTOGRAM_WITH_STARTUP_TEMPERATURE(
+        UMA_HISTOGRAM_TIME_IN_MINUTES_MONTH_RANGE,
+        "Startup.TimeSinceLastStartup", time_since_last_startup.InMinutes());
+  }
+
+  // Write the timestamp of the current startup in |pref_service|.
+  pref_service->SetInt64(kLastStartupTimestampPref,
+                         process_start_time.ToInternalValue());
+}
+
 void RecordBrowserWindowDisplay(const base::TimeTicks& ticks) {
   static bool is_first_call = true;
   if (!is_first_call || ticks.is_null())