[ios] Extend BrowserList API.

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

Index: ios/shared/chrome/browser/ui/browser_list/browser_list.mm
diff --git a/ios/shared/chrome/browser/ui/browser_list/browser_list.mm b/ios/shared/chrome/browser/ui/browser_list/browser_list.mm
index bb49ea6cefc25bb6b112aadc510ab2808ed3539e..7bf86f26623042bba6dfd9dffd72c47c71e6a75d 100644
--- a/ios/shared/chrome/browser/ui/browser_list/browser_list.mm
+++ b/ios/shared/chrome/browser/ui/browser_list/browser_list.mm
@@ -39,20 +39,23 @@ BrowserList* BrowserList::FromBrowserState(
   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 < GetBrowserCount();
+  return 0 <= index && index < count();
 }
 
-Browser* BrowserList::GetBrowserAtIndex(int index) const {
+Browser* BrowserList::GetBrowserAt(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();
@@ -62,3 +65,5 @@ void BrowserList::CloseBrowserAtIndex(int index) {
   DCHECK(ContainsIndex(index));
   browsers_.erase(browsers_.begin() + index);
 }
+
+const int BrowserList::kInvalidIndex;