[New Tab Page] Change the mechanism to intercept online NTP errors

chrome/browser/ui/search/new_tab_page_interceptor_service.cc

+// Copyright 2015 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/search/new_tab_page_interceptor_service.h"
+
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/search/search.h"
+#include "chrome/browser/search_engines/template_url_service_factory.h"
+#include "chrome/browser/ui/search/new_tab_page_interceptor.h"
+#include "components/search_engines/template_url_service.h"
+#include "content/public/browser/browser_thread.h"
+
+NewTabPageInterceptorService::NewTabPageInterceptorService(Profile* profile)
+    : profile_(profile),
+      template_url_service_(TemplateURLServiceFactory::GetForProfile(profile)) {
+  DCHECK(profile_);
+  if (template_url_service_)
+    template_url_service_->AddObserver(this);
+}
+
+NewTabPageInterceptorService::~NewTabPageInterceptorService() {
+  if (template_url_service_)
+    template_url_service_->RemoveObserver(this);
+}
+
+void NewTabPageInterceptorService::OnTemplateURLServiceChanged() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);

[Mathieu, 2015/01/21 21:29:39]

kmadhusu@: Do you think it's worth replicating the logic in
InstantService::OnTemplateURLServiceChanged() here? The code is much simpler
here, but not sure how often it'll trigger for nothing. What do you think?

[kmadhusu, 2015/01/22 20:06:30]

I looked at the latest patch. These changes seems reasonable. I will do a quick
test just to make sure everything works as expected. 

[kmadhusu, 2015/01/23 00:59:32]

Tested the latest patch. NTP interceptor works as expected.

+  GURL new_tab_page_url(chrome::GetNewTabPageURL(profile_));
+  content::BrowserThread::PostTask(
+      content::BrowserThread::IO, FROM_HERE,
+      base::Bind(&NewTabPageInterceptor::SetNewTabPageURL, interceptor_,
+                 new_tab_page_url));
+}
+
+scoped_ptr<net::URLRequestInterceptor>
+NewTabPageInterceptorService::CreateInterceptor() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  scoped_ptr<NewTabPageInterceptor> interceptor(
+      new NewTabPageInterceptor(chrome::GetNewTabPageURL(profile_)));
+  interceptor_ = interceptor->GetWeakPtr();
+  return interceptor.Pass();
+}