Implements AddStartupEventsForTelemetry() in startup_metric_utils.cc for in-coming startup telemetry

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 122326e95daff16a888d4106c7d148d12afeb4d7..3025e2dc618dd76b176eff6220c4db44e5f6eb75 100644
--- a/components/startup_metric_utils/browser/startup_metric_utils.cc
+++ b/components/startup_metric_utils/browser/startup_metric_utils.cc
@@ -284,6 +284,8 @@ void RecordMainEntryTimeHistogram() {
           (browser_main_entry_time_raw_ms >> 1) & kLower31BitsMask);
 
   // A timestamp is a 64 bit value, yet histograms can only store 32 bits.
+  // TODO(gabadie): Once startup_with_url.* benchmarks are replaced by
+  //    startup_with_url2.*, remove this dirty hack.
   LOCAL_HISTOGRAM_TIMES("Startup.BrowserMainEntryTimeAbsoluteHighWord",
       browser_main_entry_time_raw_ms_high_word);
   LOCAL_HISTOGRAM_TIMES("Startup.BrowserMainEntryTimeAbsoluteLowWord",
@@ -306,6 +308,25 @@ base::Time ExeMainEntryPointTime() {
   return base::Time();
 }
 
+// Traces process creation and main entry point mark events.
+void TraceMissingStartupInstantEvents() {

[gab, 2015/11/10 19:30:53]

Would prefer an even more specific name, e.g. AddStartupEventsForTelemetry().

With a description like:

// Records "instant" trace events for global timings observed by telemetry.


(if we ever need something more generic, we should add it to the macros in this
file, but for now a dedicated helper sgtm)

[gabadie, 2015/11/12 08:57:20]

Done.

+  static bool is_first_call = true;
+  if (!is_first_call)
+    return;
+  is_first_call = false;

[gab, 2015/11/10 19:30:53]

This method only be called once hence you shouldn't need to do this check.

[gabadie, 2015/11/12 08:57:20]

Good catch! Done.

+
+  DCHECK(!g_process_creation_time.Get().is_null());
+  DCHECK(!g_main_entry_point_time.Get().is_null());
+
+  TRACE_EVENT_INSTANT_WITH_TIMESTAMP("startup",

[gab, 2015/11/10 19:30:53]

Suggest running "git cl format", the argument alignment as-is is incorrect.

[gabadie, 2015/11/12 08:57:20]

My bad. Done.

+      "Startup.BrowserProcessCreation", 0,
+      StartupTimeToTimeTicks(g_process_creation_time.Get()).ToInternalValue());

[gab, 2015/11/10 19:30:53]

FYI: Very soon this should use g_process_creation_ticks instead (i.e. whenever
https://codereview.chromium.org/1425263003/ completes its journey through CQ).

[gabadie, 2015/11/12 08:57:20]

Done.

+
+  TRACE_EVENT_INSTANT_WITH_TIMESTAMP("startup",
+      "Startup.BrowserMainEntryPoint",  0,
+      StartupTimeToTimeTicks(g_main_entry_point_time.Get()).ToInternalValue());

[gab, 2015/11/10 19:30:53]

g_main_entry_point_ticks for this too

[gabadie, 2015/11/12 08:57:20]

Done.

+}
+
 }  // namespace
 
 bool WasNonBrowserUIDisplayed() {
@@ -336,6 +357,7 @@ void RecordExeMainEntryPointTime(const base::Time& time) {
 
 void RecordBrowserMainMessageLoopStart(const base::Time& time,
                                        bool is_first_run) {
+  TraceMissingStartupInstantEvents();
   RecordHardFaultHistogram(is_first_run);
   RecordMainEntryTimeHistogram();