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

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 4c903959166b8ce50ce21417701a0f86776bec50..fd43889d64668e1b28674ec964d84a078f9c847f 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1485,6 +1485,11 @@ const FeatureEntry kFeatureEntries[] = {
      flag_descriptions::kShowAutofillSignaturesName,
      flag_descriptions::kShowAutofillSignaturesDescription, kOsAll,
      SINGLE_VALUE_TYPE(autofill::switches::kShowAutofillSignatures)},
+
+    {"enable-predictor-preconnect", flag_descriptions::kPredictorPreconnectName,
+     flag_descriptions::kPredictorPreconnectDescription, kOsAll,
+     FEATURE_VALUE_TYPE(features::kPredictorPreconnect)},
+
     {"affiliation-based-matching",
      flag_descriptions::kAffiliationBasedMatchingName,
      flag_descriptions::kAffiliationBasedMatchingDescription, kOsAll,