Convert some of TabModel logic to WebStateListObservers.

ios/chrome/browser/tabs/tab_model_tab_model_observers_bridge.h

Index: ios/chrome/browser/tabs/tab_model_tab_model_observers_bridge.h
diff --git a/ios/chrome/browser/tabs/tab_model_tab_model_observers_bridge.h b/ios/chrome/browser/tabs/tab_model_tab_model_observers_bridge.h
new file mode 100644
index 0000000000000000000000000000000000000000..173f7d37ac6c35d5224cad58478d97f4e32e5b60
--- /dev/null
+++ b/ios/chrome/browser/tabs/tab_model_tab_model_observers_bridge.h
@@ -0,0 +1,24 @@
+// 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.
+
+#ifndef IOS_CHROME_BROWSER_TABS_TAB_MODEL_TAB_MODEL_OBSERVERS_BRIDGE_H_
+#define IOS_CHROME_BROWSER_TABS_TAB_MODEL_TAB_MODEL_OBSERVERS_BRIDGE_H_
+
+#import "ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.h"
+
+@class TabModel;
+@class TabModelObservers;
+
+// Bridge WebStateListObserver events to TabModelObservers.
+@interface TabModelTabModelObserversBridge : NSObject<WebStateListObserver>

[marq (ping after 24h), 2017/02/13 17:06:54]

Can this just be TabModelObserversBridge?

[sdefresne, 2017/02/14 17:19:38]

Done.

I've kept this object in Objective-C as it allows me to use ARC for
implementation. Changing this to C++ would require moving the __weak annotated
pointer into the header file which does not work with ARC, thus requiring the
use of __unsafe_unretained. As the class is short lived, I think using
Objective-C makes the code simpler.

+
+- (instancetype)initWithTabModel:(TabModel*)tabModel
+               tabModelObservers:(TabModelObservers*)tabModelObservers
+    NS_DESIGNATED_INITIALIZER;
+
+- (instancetype)init NS_UNAVAILABLE;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_TABS_TAB_MODEL_TAB_MODEL_OBSERVERS_BRIDGE_H_