Revert 251503 "Implement inline signin with iframe"

chrome/browser/ui/webui/signin/inline_login_ui.cc

Index: chrome/browser/ui/webui/signin/inline_login_ui.cc
===================================================================
--- chrome/browser/ui/webui/signin/inline_login_ui.cc	(revision 251944)
+++ chrome/browser/ui/webui/signin/inline_login_ui.cc	(working copy)
@@ -4,7 +4,6 @@
 
 #include "chrome/browser/ui/webui/signin/inline_login_ui.h"
 
-#include "chrome/browser/extensions/extension_web_contents_observer.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/url_constants.h"
 #include "content/public/browser/web_ui.h"
@@ -23,7 +22,6 @@
 content::WebUIDataSource* CreateWebUIDataSource() {
   content::WebUIDataSource* source =
         content::WebUIDataSource::Create(chrome::kChromeUIChromeSigninHost);
-  source->OverrideContentSecurityPolicyFrameSrc("frame-src chrome-extension:;");
   source->SetUseJsonJSFormatV2();
   source->SetJsonPath("strings.js");
 
@@ -50,8 +48,7 @@
   // Required for intercepting extension function calls when the page is loaded
   // in a bubble (not a full tab, thus tab helpers are not registered
   // automatically).
-  extensions::ExtensionWebContentsObserver::CreateForWebContents(
-      web_ui->GetWebContents());
+  extensions::TabHelper::CreateForWebContents(web_ui->GetWebContents());
 #endif
 }