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

chrome/browser/net/predictor_tab_helper.cc

Index: chrome/browser/net/predictor_tab_helper.cc
diff --git a/chrome/browser/net/predictor_tab_helper.cc b/chrome/browser/net/predictor_tab_helper.cc
index 20f4157dc7a7f79007760e8283694255455f9516..d8c0c4a579b010d0fab10bbb46eda85ea9a62673 100644
--- a/chrome/browser/net/predictor_tab_helper.cc
+++ b/chrome/browser/net/predictor_tab_helper.cc
@@ -5,11 +5,13 @@
 #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"
@@ -38,6 +40,8 @@ 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()))
@@ -55,6 +59,8 @@ void PredictorTabHelper::DidStartNavigation(
 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())
@@ -78,6 +84,7 @@ void PredictorTabHelper::DocumentOnLoadCompletedInMainFrame() {
 }
 
 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());