[ios] Extend BrowserList API.

ios/shared/chrome/browser/ui/browser_list/browser_list.mm

 // 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.
 
 #import "ios/shared/chrome/browser/ui/browser_list/browser_list.h"
 
 #include <stdint.h>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 21 matching lines @@
       browser_state->GetUserData(&kBrowserListKey);
   if (!data) {
     browser_state->SetUserData(&kBrowserListKey,
                                base::MakeUnique<BrowserList>(browser_state));
     data = browser_state->GetUserData(&kBrowserListKey);
   }
   DCHECK(data);
   return static_cast<BrowserList*>(data);
 }
 
-int BrowserList::GetBrowserCount() const {
-  DCHECK_LE(browsers_.size(), static_cast<size_t>(INT_MAX));
-  return static_cast<int>(browsers_.size());
+int BrowserList::ContainsIndex(int index) const {
+  return 0 <= index && index < count();
 }
 
-int BrowserList::ContainsIndex(int index) const {
-  return 0 <= index && index < GetBrowserCount();
+Browser* BrowserList::GetBrowserAt(int index) const {
+  DCHECK(ContainsIndex(index));
+  return browsers_[index].get();
 }
 
-Browser* BrowserList::GetBrowserAtIndex(int index) const {
-  DCHECK(ContainsIndex(index));
-  return browsers_[index].get();
+int BrowserList::GetIndexOfBrowser(const Browser* browser) const {
+  for (int index = 0; index < count(); ++index) {
+    if (browsers_[index].get() == browser)
+      return index;
+  }
+  return kInvalidIndex;
 }
 
 Browser* BrowserList::CreateNewBrowser() {
   browsers_.push_back(base::MakeUnique<Browser>(browser_state_));
   return browsers_.back().get();
 }
 
 void BrowserList::CloseBrowserAtIndex(int index) {
   DCHECK(ContainsIndex(index));
   browsers_.erase(browsers_.begin() + index);
 }
+
+const int BrowserList::kInvalidIndex;