predictors: Add browsertest that tests prefetching.

chrome/browser/predictors/resource_prefetcher_manager.cc

 // 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/predictors/resource_prefetcher_manager.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
@@ skipping 64 matching lines @@
   if (it != prefetcher_map_.end() &&
       it->second->main_frame_url() == main_frame_url) {
     it->second->Stop();
   }
 }
 
 void ResourcePrefetcherManager::ResourcePrefetcherFinished(
     ResourcePrefetcher* resource_prefetcher) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
 
-  const std::string key = resource_prefetcher->main_frame_url().host();
+  const GURL main_frame_url = resource_prefetcher->main_frame_url();
+  const std::string key = main_frame_url.host();
   auto it = prefetcher_map_.find(key);
   DCHECK(it != prefetcher_map_.end());
   prefetcher_map_.erase(it);
+
+  BrowserThread::PostTask(

[alexilin, 2016/12/06 12:44:17]

Probably we don't want to send this message to other thread for non-testing
code. WDYT?

+      BrowserThread::UI, FROM_HERE,
+      base::Bind(&ResourcePrefetchPredictor::OnPrefetchingFinished,
+                 base::Unretained(predictor_), main_frame_url));

[alexilin, 2016/12/06 12:44:17]

I'm not sure that base::Unretained is safe here. PTAL.

 }
 
 net::URLRequestContext* ResourcePrefetcherManager::GetURLRequestContext() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
 
   return context_getter_->GetURLRequestContext();
 }
 
 }  // namespace predictors