[clean] Use CommandDispatcher to show/close Settings.

ios/shared/chrome/browser/ui/commands/command_dispatcher.mm

 // Copyright 2017 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/shared/chrome/browser/ui/commands/command_dispatcher.h"
 
 #include <unordered_map>
 #include <vector>
 
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @implementation CommandDispatcher {
   // Stores which target to forward to for a given selector.
   std::unordered_map<SEL, __weak id> _forwardingTargets;
 }
 
 - (void)startDispatchingToTarget:(id)target forSelector:(SEL)selector {
   DCHECK(_forwardingTargets.find(selector) == _forwardingTargets.end());
 
   _forwardingTargets[selector] = target;
 }
 
+- (void)stopDispatchingForSelector:(SEL)selector {
+  _forwardingTargets.erase(selector);
+}
+
 // |-stopDispatchingToTarget| should be called much less often than
 // |-forwardingTargetForSelector|, so removal is intentionally O(n) in order
 // to prioritize the speed of lookups.
 - (void)stopDispatchingToTarget:(id)target {
   std::vector<SEL> selectorsToErase;
   for (auto& kv : _forwardingTargets) {
     if (kv.second == target) {
       selectorsToErase.push_back(kv.first);
     }
   }
 
   for (auto* selector : selectorsToErase) {
-    _forwardingTargets.erase(selector);
+    [self stopDispatchingForSelector:selector];
   }
 }
 
 #pragma mark - NSObject
 
 // Overridden to forward messages to registered handlers.
 - (id)forwardingTargetForSelector:(SEL)selector {
   auto target = _forwardingTargets.find(selector);
   if (target != _forwardingTargets.end()) {
     return target->second;
   }
   return [super forwardingTargetForSelector:selector];
 }
 
 @end