[Not for review] Add TRACE_EVENTs and chrome://flags for preconnect

chrome/browser/net/predictor_tab_helper.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/net/predictor_tab_helper.h"
 
 #include "base/feature_list.h"
+#include "base/trace_event/trace_event.h"
 #include "chrome/browser/net/predictor.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/url_constants.h"
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/common/browser_side_navigation_policy.h"
+#include "content/public/common/content_features.h"
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/profiles/profile_helper.h"
 #endif  // defined(OS_CHROMEOS)
 
 DEFINE_WEB_CONTENTS_USER_DATA_KEY(chrome_browser_net::PredictorTabHelper);
 
 namespace chrome_browser_net {
 
 namespace {
 
 // Triggers the preconnector on renderer-initiated navigations. This captures
 // more navigations.
 const base::Feature kPreconnectMore{"PreconnectMore",
                                     base::FEATURE_DISABLED_BY_DEFAULT};
 
 }  // namespace
 
 PredictorTabHelper::PredictorTabHelper(content::WebContents* web_contents)
     : content::WebContentsObserver(web_contents),
       predicted_from_pending_entry_(false) {
 }
 
 PredictorTabHelper::~PredictorTabHelper() {
 }
 
 void PredictorTabHelper::DidStartNavigation(
     content::NavigationHandle* navigation_handle) {
+  if (!base::FeatureList::IsEnabled(features::kPredictorPreconnect))
+    return;
   if (!base::FeatureList::IsEnabled(kPreconnectMore) &&
       (!content::IsBrowserSideNavigationEnabled() ||
        navigation_handle->IsRendererInitiated()))
     return;
   // Subframe navigations are handled in WitnessURLRequest.
   if (!navigation_handle->IsInMainFrame())
     return;
   if (predicted_from_pending_entry_) {
     predicted_from_pending_entry_ = false;
     return;
   }
   PreconnectUrl(navigation_handle->GetURL());
 }
 
 void PredictorTabHelper::DidStartNavigationToPendingEntry(
     const GURL& url,
     content::ReloadType reload_type) {
+  if (!base::FeatureList::IsEnabled(features::kPredictorPreconnect))
+    return;
   // This method isn't needed with PlzNavigate (see comment in header for
   // predicted_from_pending_entry_)
   if (content::IsBrowserSideNavigationEnabled())
     return;
 
   // The standard way to preconnect based on navigation.
   PreconnectUrl(url);
   predicted_from_pending_entry_ = true;
 }
 
 void PredictorTabHelper::DocumentOnLoadCompletedInMainFrame() {
   Profile* profile =
       Profile::FromBrowserContext(web_contents()->GetBrowserContext());
   Predictor* predictor = profile->GetNetworkPredictor();
 #if defined(OS_CHROMEOS)
   if (chromeos::ProfileHelper::IsSigninProfile(profile))
     return;
 #endif
   if (predictor)
     predictor->SaveStateForNextStartup();
 }
 
 void PredictorTabHelper::PreconnectUrl(const GURL& url) {
+  TRACE_EVENT1("net", "PredictorTabHelper::PreconnectUrl", "url", url.spec());
   Profile* profile =
       Profile::FromBrowserContext(web_contents()->GetBrowserContext());
   Predictor* predictor(profile->GetNetworkPredictor());
   if (predictor && url.SchemeIsHTTPOrHTTPS())
     predictor->PreconnectUrlAndSubresources(url, GURL());
 }
 
 }  // namespace chrome_browser_net