Introduce BrowserList and Browser classes for iOS.

ios/clean/chrome/browser/model/browser_list.mm

Index: ios/clean/chrome/browser/model/browser_list.mm
diff --git a/ios/clean/chrome/browser/model/browser_list.mm b/ios/clean/chrome/browser/model/browser_list.mm
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+++ b/ios/clean/chrome/browser/model/browser_list.mm
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+// 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/clean/chrome/browser/model/browser_list.h"
+
+#include <stdint.h>
+
+#include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "ios/chrome/browser/browser_state/chrome_browser_state.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace {
+const char kBrowserListKey = 0;
+}
+
+BrowserList::BrowserList(ios::ChromeBrowserState* browser_state)
+    : browser_state_(browser_state) {
+  DCHECK(browser_state_);
+}
+
+BrowserList::~BrowserList() = default;
+
+// static
+BrowserList* BrowserList::FromBrowserState(
+    ios::ChromeBrowserState* browser_state) {
+  base::SupportsUserData::Data* data =
+      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 < GetBrowserCount();
+}
+
+Browser* BrowserList::GetBrowserAtIndex(int index) const {
+  DCHECK(ContainsIndex(index));
+  return browsers_[index].get();
+}
+
+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);
+}