Child coordinators notify their parent upon -start and -stop.

ios/clean/chrome/browser/browser_coordinator.mm

Index: ios/clean/chrome/browser/browser_coordinator.mm
diff --git a/ios/clean/chrome/browser/browser_coordinator.mm b/ios/clean/chrome/browser/browser_coordinator.mm
index 4c7af0135dd761155086e43f6fde736500bfa6e3..828ae8d4f6c66cd4e69feb3565c4e17be8c95f16 100644
--- a/ios/clean/chrome/browser/browser_coordinator.mm
+++ b/ios/clean/chrome/browser/browser_coordinator.mm
@@ -43,11 +43,11 @@
 #pragma mark - Public API
 
 - (void)start {
-  // Default implementation is a no-op.
+  [self.parentCoordinator childCoordinatorDidStart:self];
 }
 
 - (void)stop {
-  // Default implementation is a no-op.
+  [self.parentCoordinator childCoordinatorWillStop:self];
 }
 
 @end
@@ -122,4 +122,12 @@
   coordinator.parentCoordinator = nil;
 }
 
+- (void)childCoordinatorDidStart:(BrowserCoordinator*)childCoordinator {
+  // Default implementation is a no-op.
+}
+
+- (void)childCoordinatorWillStop:(BrowserCoordinator*)childCoordinator {
+  // Default implementation is a no-op.
+}
+
 @end