Set process phases in the StackSamplingProfiler.

components/metrics/proto/execution_context.proto

 // Copyright 2016 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 option java_outer_classname = "ExecutionContextProtos";
 option java_package = "org.chromium.components.metrics";
 
@@ skipping 36 matching lines @@
   RENDER_THREAD = 9;
   UTILITY_THREAD = 10;
 }
 
 // Process phases, or where in the lifetime of the process it is such as
 // startup, normal operation, shutdown, etc. These don't necessarily occur in
 // the order defined here so it's fine to add new ones to further segregrate
 // the lifetime of a process.
 enum ProcessPhase {
   // The browser's main message loop has been started.
-  // Based on histogram Startup.BrowserMainRunnerImplInitializeStep2Time.
+  // Based on histogram Startup.BrowserMainRunnerImplInitializeStep1Time.

[Mike Wittman, 2016/12/01 16:40:33]

This should be based on Startup.BrowserMessageLoopStartTime, which is the most
commonly-used metric for this purpose.

[bcwhite, 2016/12/01 17:59:54]

Done.

   MAIN_LOOP_START = 0;
 
   // The beginning of navigation in the first web contents' main frame.
   // Based on histogram Startup.FirstWebContents.MainNavigationStart.
   MAIN_NAVIGATION_START = 1;
 
   // The navigation is committed (first bytes received) in the first web
   // contents' main frame.
   // Based on histogram Startup.FirstWebContents.MainNavigationFinished.
   MAIN_NAVIGATION_FINISHED = 2;
 
   // First non-empty paint of the first web contents.
   // Based on histogram Startup.FirstWebContents.NonEmptyPaint2.
   FIRST_NONEMPTY_PAINT = 3;
 
   // Process shutdown has begun.
   SHUTDOWN_START = 4;
 }