[ios] Create a TabStrip Mediator.

This CL creates a mediator for connecting TabStrip to WebStateList and
as for now the TabStrip shows the number of tabs open.

Bug: 1136834,1128249
Change-Id: I9082b675f88a30002f9113a363b1b1e7c2b62465
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461010
Commit-Queue: Nazerke Kalidolda <nazerke@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822673}

ios/chrome/browser/ui/tab_strip/BUILD.gn

@@ -14,6 +14,7 @@ source_set("tab_strip") {
     "//ios/chrome/browser/main:public",
     "//ios/chrome/browser/ui/coordinators:chrome_coordinators",
     "//ios/chrome/browser/ui/tab_strip:tab_strip_ui",
+    "//ios/chrome/browser/web_state_list",
   ]
   frameworks = [ "UIKit.framework" ]
 }
@@ -23,14 +24,16 @@ source_set("tab_strip_ui") {
   sources = [
     "tab_strip_cell.h",
     "tab_strip_cell.mm",
+    "tab_strip_consumer.h",
+    "tab_strip_mediator.h",
+    "tab_strip_mediator.mm",
     "tab_strip_view_controller.h",
     "tab_strip_view_controller.mm",
     "tab_strip_view_layout.h",
     "tab_strip_view_layout.mm",
   ]
   deps = [
-    "//ios/chrome/browser/browser_state",
-    "//ios/chrome/browser/main:public",
+    "//ios/chrome/browser/web_state_list",
     "//ios/chrome/common/ui/colors",
   ]
   frameworks = [ "UIKit.framework" ]

ios/chrome/browser/ui/tab_strip/tab_strip_consumer.h

+// Copyright 2020 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.
+
+#ifndef IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_CONSUMER_H_
+#define IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_CONSUMER_H_
+
+#import <Foundation/Foundation.h>
+
+// TabStripConsumer sets the current appearance of the TabStrip.
+@protocol TabStripConsumer
+
+// Sets the number to tabs currently opened.
+- (void)setTabsCount:(NSUInteger)tabsCount;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_CONSUMER_H_

ios/chrome/browser/ui/tab_strip/tab_strip_coordinator.h

@@ -23,7 +23,7 @@ class Browser;
                                    browser:(Browser*)browser NS_UNAVAILABLE;
 
 // The TabStrip view controller owned by this coordinator.
-@property(nonatomic, strong) UIViewController* viewController;
+@property(nonatomic, strong, readonly) UIViewController* viewController;
 
 // The TabStrip view owned by the viewcontroller of this coordinator.
 @property(nonatomic, strong, readonly) UIView<TabStripContaining>* view;

ios/chrome/browser/ui/tab_strip/tab_strip_coordinator.mm

@@ -7,7 +7,9 @@
 #include "base/check_op.h"
 #import "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #import "ios/chrome/browser/main/browser.h"
+#import "ios/chrome/browser/ui/tab_strip/tab_strip_mediator.h"
 #import "ios/chrome/browser/ui/tab_strip/tab_strip_view_controller.h"
+#import "ios/chrome/browser/web_state_list/web_state_list.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
@@ -15,6 +17,15 @@
 
 @protocol TabStripContaining;
 
+@interface TabStripCoordinator ()
+
+// Mediator for updating the TabStrip when the WebStateList changes.
+@property(nonatomic, strong) TabStripMediator* mediator;
+
+@property TabStripViewController* tabStripViewController;
+
+@end
+
 @implementation TabStripCoordinator
 
 #pragma mark - ChromeCoordinator
@@ -25,24 +36,33 @@
 }
 
 - (void)start {
-  if (self.viewController)
+  if (self.tabStripViewController)
     return;
 
-  self.viewController = [[TabStripViewController alloc] init];
+  self.tabStripViewController = [[TabStripViewController alloc] init];
   if (@available(iOS 13, *)) {
-    self.viewController.overrideUserInterfaceStyle =
+    self.tabStripViewController.overrideUserInterfaceStyle =
         self.browser->GetBrowserState()->IsOffTheRecord()
             ? UIUserInterfaceStyleDark
             : UIUserInterfaceStyleUnspecified;
   }
+
+  self.mediator =
+      [[TabStripMediator alloc] initWithConsumer:self.tabStripViewController];
+  self.mediator.webStateList = self.browser->GetWebStateList();
 }
 
 - (void)stop {
-  self.viewController = nil;
+  self.mediator = nil;
+  self.tabStripViewController = nil;
 }
 
 #pragma mark - Properties
 
+- (UIViewController*)viewController {
+  return self.tabStripViewController;
+}
+
 - (void)setLongPressDelegate:(id<PopupMenuLongPressDelegate>)longPressDelegate {
   _longPressDelegate = longPressDelegate;
 }
@@ -54,7 +74,7 @@
 #pragma mark - Public
 
 - (void)hideTabStrip:(BOOL)hidden {
-  self.viewController.view.hidden = hidden;
+  self.tabStripViewController.view.hidden = hidden;
 }
 
 @end

ios/chrome/browser/ui/tab_strip/tab_strip_mediator.h

+// Copyright 2020 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.
+
+#ifndef IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_MEDIATOR_H_
+#define IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_MEDIATOR_H_
+
+#import <Foundation/Foundation.h>
+
+@protocol TabStripConsumer;
+class WebStateList;
+
+// This mediator used to manage model interaction for its consumer.
+@interface TabStripMediator : NSObject
+
+// The WebStateList that this mediator listens for any changes on the total
+// number of Webstates.
+@property(nonatomic, assign) WebStateList* webStateList;
+
+// Designated initializer. Initializer with a TabStripConsumer.
+- (instancetype)initWithConsumer:(id<TabStripConsumer>)consumer
+    NS_DESIGNATED_INITIALIZER;
+- (instancetype)init NS_UNAVAILABLE;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_TAB_STRIP_TAB_STRIP_MEDIATOR_H_

ios/chrome/browser/ui/tab_strip/tab_strip_mediator.mm

+// Copyright 2020 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/chrome/browser/ui/tab_strip/tab_strip_mediator.h"
+
+#import "ios/chrome/browser/ui/tab_strip/tab_strip_consumer.h"
+#import "ios/chrome/browser/web_state_list/web_state_list.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@interface TabStripMediator ()
+// The consumer for this object.
+@property(nonatomic, weak) id<TabStripConsumer> consumer;
+@end
+
+@implementation TabStripMediator
+
+- (instancetype)initWithConsumer:(id<TabStripConsumer>)consumer {
+  if (self = [super init]) {
+    _consumer = consumer;
+  }
+  return self;
+}
+
+#pragma mark - Public properties
+
+- (void)setWebStateList:(WebStateList*)webStateList {
+  _webStateList = webStateList;
+  if (_webStateList) {
+    DCHECK_GE(_webStateList->count(), 0);
+    [_consumer setTabsCount:static_cast<NSUInteger>(_webStateList->count())];
+  }
+}
+
+@end

ios/chrome/browser/ui/tab_strip/tab_strip_view_controller.h

@@ -7,10 +7,15 @@
 
 #import <UIKit/UIKit.h>
 
+#import "ios/chrome/browser/ui/tab_strip/tab_strip_consumer.h"
+
+@class TabStripMediator;
+
 // ViewController for the TabStrip. This ViewController is contained by
 // BrowserViewController. This TabStripViewController is responsible for
 // responding to the different updates in the tabstrip view.
-@interface TabStripViewController : UICollectionViewController
+@interface TabStripViewController
+    : UICollectionViewController <TabStripConsumer>
 
 - (instancetype)init NS_DESIGNATED_INITIALIZER;
 

ios/chrome/browser/ui/tab_strip/tab_strip_view_controller.mm

@@ -4,19 +4,27 @@
 
 #import "ios/chrome/browser/ui/tab_strip/tab_strip_view_controller.h"
 
+#import "base/allocator/partition_allocator/partition_alloc.h"
 #import "ios/chrome/browser/ui/tab_strip/tab_strip_cell.h"
+#import "ios/chrome/browser/ui/tab_strip/tab_strip_mediator.h"
 #import "ios/chrome/browser/ui/tab_strip/tab_strip_view_layout.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
-@implementation TabStripViewController
-
 namespace {
 static NSString* const kReuseIdentifier = @"TabView";
 }  // namespace
 
+@interface TabStripViewController ()
+// Returns the number of tabs, the value is taken from the count() of
+// the WebStateList.
+@property(nonatomic, assign) NSUInteger tabsCount;
+@end
+
+@implementation TabStripViewController
+
 - (instancetype)init {
   TabStripViewLayout* layout = [[TabStripViewLayout alloc] init];
   if (self = [super initWithCollectionViewLayout:layout]) {
@@ -37,6 +45,11 @@ static NSString* const kReuseIdentifier = @"TabView";
   return 1;
 }
 
+- (NSInteger)collectionView:(UICollectionView*)collectionView
+     numberOfItemsInSection:(NSInteger)section {
+  return _tabsCount;
+}
+
 - (UICollectionViewCell*)collectionView:(UICollectionView*)collectionView
                  cellForItemAtIndexPath:(NSIndexPath*)indexPath {
   TabStripCell* cell = (TabStripCell*)[collectionView