Add a "started" protected property to BrowserCoordinator.

ios/clean/chrome/browser/browser_coordinator.mm

 // 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.
 
 // ======                        New Architecture                         =====
 // =         This code is only used in the new iOS Chrome architecture.       =
 // ============================================================================
 
 #import "base/logging.h"
 #import "ios/clean/chrome/browser/browser_coordinator+internal.h"
 #import "ios/clean/chrome/browser/browser_coordinator.h"
 #import "ios/shared/chrome/browser/coordinator_context/coordinator_context.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @interface BrowserCoordinator ()
 // Child coordinators owned by this object.
 @property(nonatomic, strong)
     NSMutableSet<BrowserCoordinator*>* childCoordinators;
 // Parent coordinator of this object, if any.
 @property(nonatomic, readwrite, weak) BrowserCoordinator* parentCoordinator;
+@property(nonatomic, readwrite) BOOL started;
 @property(nonatomic, readwrite) BOOL overlaying;
 @end
 
 @implementation BrowserCoordinator
 
 @synthesize context = _context;
 @synthesize browser = _browser;
 @synthesize childCoordinators = _childCoordinators;
 @synthesize parentCoordinator = _parentCoordinator;
+@synthesize started = _started;
 @synthesize overlaying = _overlaying;
 
 - (instancetype)init {
   if (self = [super init]) {
     _context = [[CoordinatorContext alloc] init];
     _childCoordinators = [NSMutableSet set];
   }
   return self;
 }
 
 #pragma mark - Public API
 
 - (void)start {
+  self.started = YES;
   [self.parentCoordinator childCoordinatorDidStart:self];
 }
 
 - (void)stop {
   [self.parentCoordinator childCoordinatorWillStop:self];
+  self.started = NO;
 }
 
 @end
 
 @implementation BrowserCoordinator (Internal)
 // Concrete implementations must implement a |viewController| property.
 @dynamic viewController;
 
 - (NSSet*)children {
   return [self.childCoordinators copy];
@@ skipping 63 matching lines @@
 
 - (void)childCoordinatorDidStart:(BrowserCoordinator*)childCoordinator {
   // Default implementation is a no-op.
 }
 
 - (void)childCoordinatorWillStop:(BrowserCoordinator*)childCoordinator {
   // Default implementation is a no-op.
 }
 
 @end