customtabs: Enable resource prefetching feature by default

The CCTResourcePrefetch feature was approved for M70+ full stable roll-out
(https://crbug.com/856077). We keep the flag to be able to disable the feature
in case of emergency.

Bug: 866460
Change-Id: Ie010d5dc6062e30dbfe2c6b559ea01b52330ff36
Reviewed-on: https://chromium-review.googlesource.com/1186335Reviewed-by: Benoit L <lizeb@chromium.org>
Commit-Queue: Alexandr Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585438}

chrome/browser/android/chrome_feature_list.cc

@@ -221,7 +221,7 @@ const base::Feature kCCTRedirectPreconnect{"CCTRedirectPreconnect",
                                            base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kCCTResourcePrefetch{"CCTResourcePrefetch",
-                                         base::FEATURE_DISABLED_BY_DEFAULT};
+                                         base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kChromeDuetFeature{"ChromeDuet",
                                        base::FEATURE_DISABLED_BY_DEFAULT};