ntp_tiles: Migrate to multi-observer model

chrome/browser/search/instant_service.cc

 // Copyright 2013 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/search/instant_service.h"
 
 #include <stddef.h>
 
 #include "base/bind.h"
 #include "base/feature_list.h"
@@ skipping 85 matching lines @@
   registrar_.Add(this,
                  content::NOTIFICATION_RENDERER_PROCESS_CREATED,
                  content::NotificationService::AllSources());
   registrar_.Add(this,
                  content::NOTIFICATION_RENDERER_PROCESS_TERMINATED,
                  content::NotificationService::AllSources());
 
   if (base::FeatureList::IsEnabled(kNtpTilesFeature)) {
     most_visited_sites_ =
         ChromeMostVisitedSitesFactory::NewForProfile(profile_);
-    most_visited_sites_->SetMostVisitedURLsObserver(this, 8);
+    most_visited_sites_->AddObserver(this);

[sfiera, 2017/01/18 09:58:33]

Here, you're not doing any filtering to produce 8 tiles. I assume that means we
can provide >8 tiles to JS now. Have you tested this with the bing or yandex
NTPs?

   } else {
     top_sites_ = TopSitesFactory::GetForProfile(profile_);
     if (top_sites_) {
       top_sites_->AddObserver(this);
       // Immediately query the TopSites state.
       TopSitesChanged(top_sites_.get(),
                       history::TopSitesObserver::ChangeReason::MOST_VISITED);
     }
   }
 
@@ skipping 27 matching lines @@
   content::URLDataSource::Add(
       profile_, new FallbackIconSource(fallback_icon_service));
   content::URLDataSource::Add(
       profile_, new FaviconSource(profile_, FaviconSource::FAVICON));
   content::URLDataSource::Add(
       profile_, new LargeIconSource(fallback_icon_service, large_icon_service));
   content::URLDataSource::Add(profile_, new MostVisitedIframeSource());
 }
 
 InstantService::~InstantService() {
+  if (most_visited_sites_)
+    most_visited_sites_->RemoveObserver(this);
   if (template_url_service_)
     template_url_service_->RemoveObserver(this);
 }
 
 void InstantService::AddInstantProcess(int process_id) {
   process_ids_.insert(process_id);
 
   if (instant_io_context_.get()) {
     content::BrowserThread::PostTask(
         content::BrowserThread::IO, FROM_HERE,
@@ skipping 340 matching lines @@
 void InstantService::ResetInstantSearchPrerendererIfNecessary() {
   if (!search::ShouldPrefetchSearchResults())
     return;
 
   GURL url(search::GetSearchResultPrefetchBaseURL(profile_));
   if (!instant_prerenderer_ || instant_prerenderer_->prerender_url() != url) {
     instant_prerenderer_.reset(
         url.is_valid() ? new InstantSearchPrerenderer(profile_, url) : nullptr);
   }
 }