Move the notion of current Tab from TabModel to WebStateList.

ios/chrome/browser/tabs/tab.h

 // Copyright 2012 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_TABS_TAB_H_
 #define IOS_CHROME_BROWSER_TABS_TAB_H_
 
 #import <UIKit/UIKit.h>
 
 #include <memory>
@@ skipping 144 matching lines @@
 
 // Delegate used to show HTTP Authentication dialogs.
 @property(nonatomic, weak) id<TabDialogDelegate> dialogDelegate;
 
 // TODO(crbug.com/661663): Should this property abstract away the concept of
 // prerendering?  Maybe this can move to the TabDelegate interface.
 @property(nonatomic, assign) BOOL isPrerenderTab;
 @property(nonatomic, assign) BOOL isLinkLoadingPrerenderTab;
 @property(nonatomic, assign) BOOL isVoiceSearchResultsTab;
 
+// |YES| if the tab has finished loading.
+@property(nonatomic, readonly) BOOL loadFinished;
+
 // Creates a new tab with the given state. |opener| is nil unless another tab
 // is conceptually the parent of this tab. |openedByDOM| is YES if the page was
 // opened by DOM. |model| and |browserState| must not be nil.
 - (instancetype)initWithBrowserState:(ios::ChromeBrowserState*)browserState
                               opener:(Tab*)opener
                          openedByDOM:(BOOL)openedByDOM
                                model:(TabModel*)parentModel;
 
 // Create a new tab with given web state and tab model. All must be non-nil.
 - (instancetype)initWithWebState:(std::unique_ptr<web::WebState>)webState
@@ skipping 171 matching lines @@
 
 // Called when this tab is hidden.
 - (void)wasHidden;
 
 // Evaluates U2F result.
 - (void)evaluateU2FResultFromURL:(const GURL&)url;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_TABS_TAB_H_