Add a bottom toolbar setting.

ios/clean/chrome/browser/ui/tab/tab_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.
 
 #import "ios/clean/chrome/browser/ui/tab/tab_coordinator.h"
 
 #include <memory>
 
 #include "base/mac/foundation_util.h"
 #include "base/memory/ptr_util.h"
 #include "ios/chrome/browser/chrome_url_constants.h"
 #import "ios/clean/chrome/browser/ui/animators/zoom_transition_animator.h"
 #import "ios/clean/chrome/browser/ui/commands/tab_commands.h"
 #import "ios/clean/chrome/browser/ui/find_in_page/find_in_page_coordinator.h"
 #import "ios/clean/chrome/browser/ui/ntp/ntp_coordinator.h"
 #import "ios/clean/chrome/browser/ui/tab/tab_container_view_controller.h"
 #import "ios/clean/chrome/browser/ui/tab_strip/tab_strip_coordinator.h"
 #import "ios/clean/chrome/browser/ui/toolbar/toolbar_coordinator.h"
 #import "ios/clean/chrome/browser/ui/web_contents/web_coordinator.h"
 #import "ios/shared/chrome/browser/ui/browser_list/browser.h"
 #import "ios/shared/chrome/browser/ui/commands/command_dispatcher.h"
 #import "ios/shared/chrome/browser/ui/coordinators/browser_coordinator+internal.h"
 #import "ios/web/public/web_state/web_state.h"
 #import "ios/web/public/web_state/web_state_observer_bridge.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
-namespace {
-// Placeholder "experiment" flag. Change this to YES to have the toolbar at the
-// bottom.
-const BOOL kUseBottomToolbar = NO;
-}  // namespace
-
 @interface TabCoordinator ()<CRWWebStateObserver,
                              TabCommands,
                              UIViewControllerTransitioningDelegate>
 @property(nonatomic, strong) TabContainerViewController* viewController;
 @property(nonatomic, weak) NTPCoordinator* ntpCoordinator;
 @property(nonatomic, weak) WebCoordinator* webCoordinator;
 @end
 
 @implementation TabCoordinator {
   std::unique_ptr<web::WebStateObserverBridge> _webStateObserver;
@@ skipping 46 matching lines @@
   if (self.webState->GetLastCommittedURL() == GURL(kChromeUINewTabURL)) {
     self.viewController.contentViewController =
         self.ntpCoordinator.viewController;
   }
 
   [super start];
 }
 
 - (void)stop {
   [super stop];
+  for (BrowserCoordinator* child in self.children) {
+    [self removeChildCoordinator:child];
+  }
   _webStateObserver.reset();
   [self.browser->dispatcher() stopDispatchingToTarget:self];
 }
 
 - (void)childCoordinatorDidStart:(BrowserCoordinator*)childCoordinator {
   if ([childCoordinator isKindOfClass:[ToolbarCoordinator class]]) {
     self.viewController.toolbarViewController = childCoordinator.viewController;
   } else if ([childCoordinator isKindOfClass:[WebCoordinator class]] ||
              [childCoordinator isKindOfClass:[NTPCoordinator class]]) {
     self.viewController.contentViewController = childCoordinator.viewController;
@@ skipping 14 matching lines @@
   }
 }
 
 - (BOOL)canAddOverlayCoordinator:(BrowserCoordinator*)overlayCoordinator {
   // This coordinator will always accept overlay coordinators.
   return YES;
 }
 
 #pragma mark - Experiment support
 
-// Create and return a new view controller for use as a tab container;
+- (BOOL)usesBottomToolbar {
+  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+  NSString* bottomToolbarPreference =
+      [defaults stringForKey:@"EnableBottomToolbar"];
+  return [bottomToolbarPreference isEqualToString:@"Enabled"];
+}
+
+// Creates and returns a new view controller for use as a tab container;
 // experimental configurations determine which subclass of
 // TabContainerViewController to return.
 - (TabContainerViewController*)newTabContainer {
-  if (kUseBottomToolbar) {
+  if ([self usesBottomToolbar]) {
     return [[BottomToolbarTabViewController alloc] init];
   }
   return [[TopToolbarTabViewController alloc] init];
 }
 
 #pragma mark - CRWWebStateObserver
 
 // This will eventually be called in -didFinishNavigation and perhaps as an
 // optimization in some equivalent to loadURL.
 - (void)webState:(web::WebState*)webState
@@ skipping 38 matching lines @@
   return animator;
 }
 
 #pragma mark - TabCommands
 
 - (void)loadURL:(web::NavigationManager::WebLoadParams)params {
   self.webState->GetNavigationManager()->LoadURLWithParams(params);
 }
 
 @end