Use TimeTicks as much as possible in startup_metric_utils.

components/startup_metric_utils/browser/startup_metric_utils.h

 // Copyright 2013 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 COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_STARTUP_METRIC_UTILS_H_
 #define COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_STARTUP_METRIC_UTILS_H_
 
 #include <string>
 
 #include "base/time/time.h"
 
-// Utility functions to support metric collection for browser startup.
+// Utility functions to support metric collection for browser startup. Timings
+// should use TimeTicks as much as possible. OS-provided timings are still
+// received as Time but are converted to TimeTicks as soon as possible as well

[fdoray, 2015/11/09 21:27:16]

The "as well" sounds weird to me. But I trust you English skills better than
mine.

[gab, 2015/11/10 01:25:29]

Agreed, re-worded entire comment.

+// (while the likelihood of a skew between the two basis is as low as possible).
+// See crbug.com/544131 for reasoning.
 
 namespace startup_metric_utils {
 
 // An enumeration of startup temperatures. This must be kept in sync with the
 // UMA StartupType enumeration defined in histograms.xml.
 enum StartupTemperature {
   // The startup was a cold start: nearly all of the Chrome binaries and
   // resources were brought into memory using hard faults.
   COLD_STARTUP_TEMPERATURE = 0,
   // The startup was a warm start: the Chrome binaries and resources were
@@ skipping 29 matching lines @@
 // In Mojo, the entry point time is the time at which the shell starts.
 void RecordMainEntryPointTime(const base::Time& time);
 
 // Call this with the time when the executable is loaded and main() is entered.
 // Can be different from |RecordMainEntryPointTime| when the startup process is
 // contained in a separate dll, such as with chrome.exe / chrome.dll on Windows.
 void RecordExeMainEntryPointTime(const base::Time& time);
 
 // Call this with the time recorded just before the message loop is started.
 // |is_first_run| - is the current launch part of a first run.
-void RecordBrowserMainMessageLoopStart(const base::Time& time,
+void RecordBrowserMainMessageLoopStart(const base::TimeTicks& ticks,
                                        bool is_first_run);
 
 // Call this with the time when the first browser window became visible.
-void RecordBrowserWindowDisplay(const base::Time& time);
+void RecordBrowserWindowDisplay(const base::TimeTicks& ticks);
 
 // Call this with the time delta that the browser spent opening its tabs.
 void RecordBrowserOpenTabsDelta(const base::TimeDelta& delta);
 
 // Call this with the time when the first web contents loaded its main frame,
 // only if the first web contents was unimpended in its attempt to do so.
-void RecordFirstWebContentsMainFrameLoad(const base::Time& time);
+void RecordFirstWebContentsMainFrameLoad(const base::TimeTicks& ticks);
 
 // Call this with the time when the first web contents loaded its main frame.
 // This records an old stat kept for comparison purposes until M49.
-void RecordDeprecatedFirstWebContentsMainFrameLoad(const base::Time& time);
+void RecordDeprecatedFirstWebContentsMainFrameLoad(
+    const base::TimeTicks& ticks);
 
 // Call this with the time when the first web contents had a non-empty paint,
 // only if the first web contents was unimpended in its attempt to do so.
-void RecordFirstWebContentsNonEmptyPaint(const base::Time& time);
+void RecordFirstWebContentsNonEmptyPaint(const base::TimeTicks& ticks);
 
 // Call this with the time when the first web contents had a non-empty paint.
 // This records an old stat kept for comparison purposes until M49.
-void RecordDeprecatedFirstWebContentsNonEmptyPaint(const base::Time& time);
+void RecordDeprecatedFirstWebContentsNonEmptyPaint(
+    const base::TimeTicks& ticks);
 
 // Call this with the time when the first web contents began navigating its main
 // frame.
-void RecordFirstWebContentsMainNavigationStart(const base::Time& time);
+void RecordFirstWebContentsMainNavigationStart(const base::TimeTicks& ticks);
 
 // Call this with the time when the first web contents successfully committed
 // its navigation for the main frame.
-void RecordFirstWebContentsMainNavigationFinished(const base::Time& time);
+void RecordFirstWebContentsMainNavigationFinished(const base::TimeTicks& ticks);
 
 // Returns the startup type. This is only currently supported on the Windows
 // platform and will simply return UNCERTAIN_STARTUP_TYPE on other platforms.
 // This is only valid after a call to RecordBrowserMainMessageLoopStart().
 StartupTemperature GetStartupTemperature();
 
 }  // namespace startup_metric_utils
 
 #endif  // COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_STARTUP_METRIC_UTILS_H_