[Reland] Enable AutoResize for Constrained Web Dialogs for Mac.

chrome/browser/ui/cocoa/login_prompt_cocoa.mm

Index: chrome/browser/ui/cocoa/login_prompt_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/login_prompt_cocoa.mm b/chrome/browser/ui/cocoa/login_prompt_cocoa.mm
index 2c24253b334721bc3a2796c18c224ea5a2dd3e6e..cd1a8443d4d47ffc109ceaa0ae3dd82e0fc61451 100644
--- a/chrome/browser/ui/cocoa/login_prompt_cocoa.mm
+++ b/chrome/browser/ui/cocoa/login_prompt_cocoa.mm
@@ -80,8 +80,8 @@ class LoginHandlerMac : public LoginHandler,
     base::scoped_nsobject<CustomConstrainedWindowSheet> sheet(
         [[CustomConstrainedWindowSheet alloc]
             initWithCustomWindow:[sheet_controller_ window]]);
-    constrained_window_.reset(new ConstrainedWindowMac(
-        this, requesting_contents, sheet));
+    constrained_window_ = CreateAndShowWebModalDialogMac(
+        this, requesting_contents, sheet);
 
     NotifyAuthNeeded();
   }