ServiceWorkerOnUI: Add Chrome flag.

This will make it easy to test the feature on Android without needing
a command-line flag.

Bug: 824858
Change-Id: I26736f1c2edbad635d9030f9d35939ace6daa799
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1833026
Commit-Queue: Matt Falkenhagen <[email protected]>
Reviewed-by: Hiroki Nakagawa <[email protected]>
Cr-Commit-Position: refs/heads/master@{#701564}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 8b6b7eb..9a0fd86 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2844,6 +2844,10 @@
      flag_descriptions::kServiceWorkerLongRunningMessageDescription, kOsAll,
      FEATURE_VALUE_TYPE(features::kServiceWorkerLongRunningMessage)},
 
+    {"enable-service-worker-on-ui", flag_descriptions::kServiceWorkerOnUIName,
+     flag_descriptions::kServiceWorkerOnUIDescription, kOsAll,
+     FEATURE_VALUE_TYPE(features::kServiceWorkerOnUI)},
+
 #if defined(OS_CHROMEOS)
     {"scheduler-configuration", flag_descriptions::kSchedulerConfigurationName,
      flag_descriptions::kSchedulerConfigurationDescription, kOsCrOS,