Add process lifetime annotations to stack samples.

components/metrics/call_stack_profile_metrics_provider.h

Index: components/metrics/call_stack_profile_metrics_provider.h
diff --git a/components/metrics/call_stack_profile_metrics_provider.h b/components/metrics/call_stack_profile_metrics_provider.h
index bd0b721c8093dc4ad9764d64c74f951932e2b9cb..74b0967943fd97cf532fdab90348f8968bff13c0 100644
--- a/components/metrics/call_stack_profile_metrics_provider.h
+++ b/components/metrics/call_stack_profile_metrics_provider.h
@@ -19,6 +19,20 @@ class ChromeUserMetricsExtension;
 // Performs metrics logging for the stack sampling profiler.
 class CallStackProfileMetricsProvider : public MetricsProvider {
  public:
+  // These phases of a process lifetime can be passed as process "phases" to
+  // StackSmaplingProfile::SetProcessPhase(). Be sure to update the translation
+  // constants at the top of the .cc file when this is changed.
+  enum Phases : int {
+    MAIN_LOOP_START,
+    MAIN_NAVIGATION_START,
+    MAIN_NAVIGATION_FINISHED,
+    FIRST_NONEMPTY_PAINT,
+
+    SHUTDOWN_START,
+
+    PHASES_MAX_VALUE
+  };
+
   CallStackProfileMetricsProvider();
   ~CallStackProfileMetricsProvider() override;