Move the notion of current Tab from TabModel to WebStateList.

ios/shared/chrome/browser/tabs/web_state_list.mm

Index: ios/shared/chrome/browser/tabs/web_state_list.mm
diff --git a/ios/shared/chrome/browser/tabs/web_state_list.mm b/ios/shared/chrome/browser/tabs/web_state_list.mm
index 77c01a6f938064f25c233665c52409ae00e1216c..ccb01f384d5eb9e3366836ba41b73f854866b49f 100644
--- a/ios/shared/chrome/browser/tabs/web_state_list.mm
+++ b/ios/shared/chrome/browser/tabs/web_state_list.mm
@@ -4,6 +4,7 @@
 
 #import "ios/shared/chrome/browser/tabs/web_state_list.h"
 
+#include <algorithm>
 #include <utility>
 
 #include "base/logging.h"
@@ -105,6 +106,12 @@ bool WebStateList::ContainsIndex(int index) const {
   return 0 <= index && index < count();
 }
 
+web::WebState* WebStateList::GetActiveWebState() const {
+  if (active_index_ != kInvalidIndex)
+    return GetWebStateAt(active_index_);
+  return nullptr;
+}
+
 web::WebState* WebStateList::GetWebStateAt(int index) const {
   DCHECK(ContainsIndex(index));
   return web_state_wrappers_[index]->web_state();
@@ -150,6 +157,9 @@ void WebStateList::InsertWebState(int index,
       base::MakeUnique<WebStateWrapper>(web_state,
                                         web_state_ownership_ == WebStateOwned));
 
+  if (active_index_ >= index)
+    ++active_index_;
+
   if (opener)
     SetOpenerOfWebStateAt(index, opener);
 
@@ -180,6 +190,16 @@ void WebStateList::MoveWebStateAt(int from_index, int to_index) {
   web_state_wrappers_.insert(web_state_wrappers_.begin() + to_index,
                              std::move(web_state_wrapper));
 
+  if (active_index_ == from_index) {
+    active_index_ = to_index;
+  } else {
+    int min = std::min(from_index, to_index);
+    int max = std::max(from_index, to_index);
+    int delta = from_index < to_index ? -1 : +1;
+    if (min <= active_index_ && active_index_ <= max)
+      active_index_ += delta;
+  }
+
   for (auto& observer : observers_)
     observer.WebStateMoved(this, web_state, from_index, to_index);
 }
@@ -206,11 +226,32 @@ void WebStateList::DetachWebStateAt(int index) {
   DCHECK(ContainsIndex(index));
   FixOpenersReferencing(index);
 
+  int new_active_index = order_controller_->DetermineNewActiveIndex(index);
+
   web::WebState* web_state = web_state_wrappers_[index]->web_state();

[rohitrao (ping after 24h), 2017/02/22 15:13:43]

What keeps ownership of this object so that it doesn't get destroyed when the
next line runs?

[sdefresne, 2017/02/23 15:43:48]

That's a really good remark. Fixed by
https://codereview.chromium.org/2710183003/.

   web_state_wrappers_.erase(web_state_wrappers_.begin() + index);
 
+  // Update the active index to prevent observer from seeing an invalid WebState
+  // as the active one but only send the WebStateActivatedAt notification after
+  // the WebStateDetachedAt one.
+  bool active_web_state_was_closed = (index == active_index_);
+  if (active_index_ > index)

[marq (ping after 24h), 2017/02/21 17:23:11]

Use {} if there's an else clause.

[sdefresne, 2017/02/21 17:29:29]

I checked the style guide [1] and it does not say to use {} if there is an else
clause. It says that if one of the two parts of the conditional uses braces,
then both need to use them. It also says that single line conditional may omit
braces. It understand the conjunction of both statement as meaning that you can
omit them in both part of the conditional if they are both single lines.

[1]: https://google.github.io/styleguide/cppguide.html#Conditionals

+    --active_index_;
+  else if (active_index_ == index)
+    active_index_ = new_active_index;
+
   for (auto& observer : observers_)
     observer.WebStateDetachedAt(this, web_state, index);
+
+  if (active_web_state_was_closed)
+    NotifyIfActiveWebStateChanged(web_state, false);
+}
+
+void WebStateList::ActivateWebStateAt(int index) {
+  DCHECK(ContainsIndex(index));
+  web::WebState* old_web_state = GetActiveWebState();
+  active_index_ = index;
+  NotifyIfActiveWebStateChanged(old_web_state, true);
 }
 
 void WebStateList::AddObserver(WebStateListObserver* observer) {
@@ -229,6 +270,18 @@ void WebStateList::FixOpenersReferencing(int index) {
   }
 }
 
+void WebStateList::NotifyIfActiveWebStateChanged(web::WebState* old_web_state,
+                                                 bool user_action) {
+  web::WebState* new_web_state = GetActiveWebState();
+  if (old_web_state == new_web_state)
+    return;
+
+  for (auto& observer : observers_) {
+    observer.WebStateActivatedAt(this, old_web_state, new_web_state,
+                                 active_index_, user_action);
+  }
+}
+
 int WebStateList::GetIndexOfNthWebStateOpenedBy(const web::WebState* opener,
                                                 int start_index,
                                                 bool use_group,