[Prerender] first contentful paint histograms.

chrome/browser/page_load_metrics/page_load_tracker.cc

 // Copyright 2016 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/page_load_metrics/page_load_tracker.h"
 
 #include <algorithm>
 #include <ostream>
 #include <string>
 #include <utility>
@@ skipping 286 matching lines @@
       abort_user_initiated_(false),
       started_in_foreground_(in_foreground),
       page_transition_(navigation_handle->GetPageTransition()),
       num_cache_requests_(0),
       num_network_requests_(0),
       user_initiated_(IsNavigationUserInitiated(navigation_handle)),
       aborted_chain_size_(aborted_chain_size),
       aborted_chain_size_same_url_(aborted_chain_size_same_url),
       embedder_interface_(embedder_interface) {
   DCHECK(!navigation_handle->HasCommitted());
-  if (embedder_interface_->IsPrerendering(
-          navigation_handle->GetWebContents())) {
-    DCHECK(!started_in_foreground_);
-    // For the time being, we do not track prerenders. See crbug.com/648338 for
-    // details.
-    StopTracking();
-    return;
-  }
-
   embedder_interface_->RegisterObservers(this);
   INVOKE_AND_PRUNE_OBSERVERS(observers_, OnStart, navigation_handle,
                              currently_committed_url, started_in_foreground_);
 }
 
 PageLoadTracker::~PageLoadTracker() {
   if (app_entered_background_) {
     RecordAppBackgroundPageLoadCompleted(true);
   }
 
@@ skipping 352 matching lines @@
   // explicitly filter these types of aborts out when deciding if the abort was
   // user initiated.
   abort_user_initiated_ = user_initiated && abort_type != ABORT_CLIENT_REDIRECT;
 
   if (is_certainly_browser_timestamp) {
     ClampBrowserTimestampIfInterProcessTimeTickSkew(&abort_time_);
   }
 }
 
 }  // namespace page_load_metrics