[ios] Add lock preventing nest batch operation on WebStateList

WebStateList is not re-entrant (already asserted by locked_)
so there is no point nesting batched operations. Add a bool
to ensure this is not the case.

Add a method to check whether a batched operation is in
progress (could be used internally to also omit sending
notification during a batched operation).

Bug: 1014526
Change-Id: I6b6dc3278312895a32898d898245f538f9a5264d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2089675
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750916}

ios/chrome/browser/web_state_list/web_state_list.h

@@ -85,6 +85,9 @@ class WebStateList {
   // Returns true if the list is currently mutating.
   bool IsMutating() const;
 
+  // Returns true if a batch operation is in progress.
+  bool IsBatchInProgress() const;
+
   // Returns the currently active WebState or null if there is none.
   web::WebState* GetActiveWebState() const;
 
@@ -276,6 +279,9 @@ class WebStateList {
   // by the returned base::AutoReset<bool>).
   bool locked_ = false;
 
+  // Lock to prevent nesting batched operations.
+  bool batch_operation_in_progress_ = false;
+
   SEQUENCE_CHECKER(sequence_checker_);
 
   DISALLOW_COPY_AND_ASSIGN(WebStateList);

ios/chrome/browser/web_state_list/web_state_list.mm

@@ -132,6 +132,11 @@ bool WebStateList::IsMutating() const {
   return locked_;
 }
 
+bool WebStateList::IsBatchInProgress() const {
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  return batch_operation_in_progress_;
+}
+
 web::WebState* WebStateList::GetActiveWebState() const {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   if (active_index_ != kInvalidIndex)
@@ -451,6 +456,10 @@ void WebStateList::RemoveObserver(WebStateListObserver* observer) {
 void WebStateList::PerformBatchOperation(
     base::OnceCallback<void(WebStateList*)> operation) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+
+  DCHECK(!batch_operation_in_progress_);
+  base::AutoReset<bool> lock(&batch_operation_in_progress_, /*locked=*/true);
+
   for (auto& observer : observers_)
     observer.WillBeginBatchOperation(this);
   if (!operation.is_null())