Enable AutoResize for Constrained Web Dialogs for Mac.

chrome/browser/ui/cocoa/profiles/user_manager_mac.mm

 // Copyright 2014 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.
 
 #include "chrome/browser/ui/cocoa/profiles/user_manager_mac.h"
 
 #include "base/mac/foundation_util.h"
 #include "chrome/app/chrome_command_ids.h"
 #import "chrome/browser/app_controller_mac.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 185 matching lines @@
         content::WebContents::CreateParams(profile)));
     window.get().contentView = reauthWebContents_->GetNativeView();
     webContentsDelegate_.reset(
        new ReauthDialogDelegate(reauthWebContents_.get(), emailAddress_));
     reauthWebContents_->SetDelegate(webContentsDelegate_.get());
 
     base::scoped_nsobject<CustomConstrainedWindowSheet> sheet(
        [[CustomConstrainedWindowSheet alloc]
            initWithCustomWindow:[self window]]);
     constrained_window_.reset(
-       new ConstrainedWindowMac(
-          webContentsDelegate_.get(), webContents_, sheet));
+        CreateAndShowWebModalDialogMac(
+            webContentsDelegate_.get(), webContents_, sheet));
 
     // The close button needs to call CloseWebContentsModalDialog() on the
     // constrained window isntead of just [window close] so grab a reference to
     // it in the title bar and change its action.
     auto closeButton = [window standardWindowButton:NSWindowCloseButton];
     [closeButton setTarget:self];
     [closeButton setAction:@selector(closeButtonClicked:)];
     [self show];
   }
 
@@ skipping 254 matching lines @@
   ProfileMetrics::LogTimeToOpenUserManager(
       base::Time::Now() - user_manager_started_showing_);
   user_manager_started_showing_ = base::Time();
 }
 
 void UserManagerMac::WindowWasClosed() {
   CloseReauthDialog();
   instance_ = NULL;
   delete this;
 }