Add process lifetime annotations to stack samples.

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 29 matching lines @@
   IO_THREAD = 6;
   DB_THREAD = 7;
 
   // GPU process thread.
   GPU_MAIN_THREAD = 8;
 
   // Renderer process threads.
   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

[Mike Wittman, 2016/11/16 22:36:10]

nit: period at end of comment (and other cases below)

[bcwhite, 2016/11/16 23:10:49]

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;
+}