[ios] Active web state observer in tab collection.

ios/clean/chrome/browser/ui/tab_strip/tab_strip_coordinator.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/clean/chrome/browser/ui/tab_strip/tab_strip_coordinator.h"
 
 #import "ios/chrome/browser/web_state_list/web_state_list.h"
+#import "ios/clean/chrome/browser/ui/commands/tab_grid_commands.h"
 #import "ios/clean/chrome/browser/ui/commands/tab_strip_commands.h"
 #import "ios/clean/chrome/browser/ui/tab_collection/tab_collection_mediator.h"
 #import "ios/clean/chrome/browser/ui/tab_strip/tab_strip_view_controller.h"
 #import "ios/shared/chrome/browser/ui/browser_list/browser.h"
 #import "ios/shared/chrome/browser/ui/commands/command_dispatcher.h"
 #include "ios/web/public/web_state/web_state.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
@@ skipping 39 matching lines @@
 }
 
 #pragma mark - TabStripCommands
 
 - (void)showTabStripTabAtIndex:(int)index {
   self.webStateList.ActivateWebStateAt(index);
 }
 
 - (void)closeTabStripTabAtIndex:(int)index {
   self.webStateList.CloseWebStateAt(index);
+  if (self.webStateList.count() == 0) {

[marq (ping after 24h), 2017/05/30 11:09:44]

if (self.webStateList.empty()) {

[edchin, 2017/06/01 23:52:29]

Done.

+    [static_cast<id<TabGridCommands>>(self.browser->dispatcher()) showTabGrid];
+  }
 }
 
 @end