Use TimeTicks as much as possible in startup_metric_utils.

mojo/services/tracing/public/interfaces/tracing.mojom

 // Copyright 2014 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.
 
 module tracing;
 
 // To participate in the tracing ecosystem, implement the TraceProvider
 // interface and connect to the tracing app. Then, when the provider's Start()
 // function is called collect tracing data and pass it back via the provided
 // TraceRecorder interface up until Stop() is called.
@@ skipping 13 matching lines @@
   // Request tracing data from all connected providers to stream to
   // |stream|.
   Start(handle<data_pipe_producer> stream, string categories);
 
   // Stop tracing and flush results to the |stream| passed in to Start().
   // Closes |stream| when all data is collected.
   StopAndFlush();
 };
 
 // These times are used to determine startup performance metrics.
-// TODO(msw): Use TimeTicks to avoid system clock changes: crbug.com/521164
 struct StartupPerformanceTimes {
   // TODO(msw): Rename to match "BrowserMainEntryTimeAbsolute" metric?
   int64 shell_process_creation_time;

[msw, 2015/11/10 18:58:38]

Hmm, I guess we might want to convert these times to ticks earlier, then add an
accessor to set the ticks instead of times in startup_metric_utils? (rather than
holding the time here for a while, then passing to startup_metric_utils when the
value is needed and only converting then... given the discussion around
converting as early as possible in crbug.com/544131) Give me a TODO?

[gab, 2015/11/10 19:18:49]

Right having the TimeTicks value ASAP is better, however for the
startup_metrics_util API I was trying to make an API that (1) works on every
platform (some of which don't know that value in TimeTicks) and (2) embeds the
Time -> TimeTicks transformation.

Happy to add a TODO for you to think of a better way, but I'm not sure about
having two entry points on startup_metrics_util.h.

   int64 shell_main_entry_point_time;
-  int64 browser_message_loop_start_time;
-  int64 browser_window_display_time;
+  int64 browser_message_loop_start_ticks;
+  int64 browser_window_display_ticks;
   int64 browser_open_tabs_time_delta;
   // TODO(msw): Rename to avoid "web contents"?
-  int64 first_web_contents_main_frame_load_time;
+  int64 first_web_contents_main_frame_load_ticks;
   // TODO(msw): Rename to match "FirstWebContents.NonEmptyPaint" metric?
-  int64 first_visually_non_empty_layout_time;
+  int64 first_visually_non_empty_layout_ticks;
 };
 
 // This interface accepts startup performance timing from a variety of sources.
 interface StartupPerformanceDataCollector {
   // These setters may be called many times, only the first time is recorded.
   SetShellProcessCreationTime(int64 time);
   SetShellMainEntryPointTime(int64 time);
-  SetBrowserMessageLoopStartTime(int64 time);
-  SetBrowserWindowDisplayTime(int64 time);
+  SetBrowserMessageLoopStartTicks(int64 ticks);
+  SetBrowserWindowDisplayTicks(int64 ticks);
   SetBrowserOpenTabsTimeDelta(int64 delta);
-  SetFirstWebContentsMainFrameLoadTime(int64 time);
-  SetFirstVisuallyNonEmptyLayoutTime(int64 time);
+  SetFirstWebContentsMainFrameLoadTicks(int64 ticks);
+  SetFirstVisuallyNonEmptyLayoutTicks(int64 ticks);
 
   // Get the currently available startup performance times.
   GetStartupPerformanceTimes() => (StartupPerformanceTimes times);
 };