Update readme files that mention the old Tab class.

TBR=marq@chromium.org

Change-Id: I4379fe780d4365b9857a9e3a8b692112152b32df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726091
Reviewed-by: Mohammad Refaat <mrefaat@chromium.org>
Commit-Queue: Mohammad Refaat <mrefaat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682280}

docs/ios/objects.md

@@ -119,9 +119,7 @@ assume that a tab helper will be available when using a WebState but
 instead should support the tab helper being unavailable.
 
 A WebState and all the attached tab helpers are sometimes called a
-tab (because they implement what the user sees and interacts with in
-a browser tab). There currently is a Tab interface but it is a legacy
-object that is deprecated and is slowly being removed. If possible,
-prefer to use WebState directly instead of Tab.
+tab because they implement what the user sees and interacts with in
+a browser tab.
 
 The corresponding object on desktop is WebContents.

ios/chrome/browser/tabs/tab_lifecycle.md

@@ -1,20 +1,13 @@
 # `Tab` lifecycle
 
-`LegacyTabHelper` creates `Tab` and keep it retained. `AttachTabHelpers`
-creates `LegacyTabHelper` first and then all the other tab helpers. The
-`AttachTabHelpers` method can be invoked on a newly created `WebState`.
-
-From that point, `LegacyTabHelper::GetTabFromWebState()` will return the
-`Tab` associated with `WebState`. That method will return `nil` before
-the call to `AttachTabHelpers`.
+`Tab` is a virtual concept that refers to the` WebState` UI. A `WebState` is created then it's 
+passed to `AttachTabHelpers` which creates all the other tab helpers. and attaches them to
+the `WebState`.
 
 ````cpp
 web::WebState::CreateParams params{...};
 std::unique_ptr<web::WebState> web_state =  web::WebState::Create(params);
 AttachTabHelper(web_state.get());
-
-Tab* tab = LegacyTabHelper::GetFromWebState(web_state.get());
-DCHECK(tab != nil);
 ````
 
 When a `WebState` is added to a `TabModel`'s `WebStateList`,
@@ -24,18 +17,7 @@ When a `WebState` is added to a `TabModel`'s `WebStateList`,
 TabModel* tab_model = ...;
 std::unique_ptr<web::WebState> web_state =  ...;
 [tab_model webStateList]->InsertWebState(0, std::move(web_state));
-Tab* tab = LegacyTabHelper::GetFromWebState(
-    [tab_model webStateList]->GetWebStateAt(0));
-DCHECK(tab != nil);
 ```
 
-`Tab` register itself as a `WebStateObserver`. When `-webStateDestroyed:`
-is invoked as part of `WebState` destruction, `Tab` destroys its state and
-should no longer be used (as `-webState` will return `nullptr`).
-
-`LegacyTabHelper` is a `WebStateUserData` thus it is destroyed after the
-`WebState` destructor completes. `LegacyTabHelper` release its reference
-to `Tab` when destroyed.
-
-It is better to only use `WebState` and to access the `Tab` via
-`LegacyTabHelper` as `Tab` will be removed in the new architecture.
+All Tab helpers are `WebStateUserData` thus they are destroyed after the
+`WebState` destructor completes.