Add a ServiceWorker Background Sync flag and check it before sending
sync events.

BUG=354112

Review URL: https://codereview.chromium.org/230613003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@263635 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index daa5076..8b9bafa0 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1577,6 +1577,13 @@
     kOsAll,
     SINGLE_VALUE_TYPE(switches::kEnableServiceWorker)
   },
+  {
+    "enable-service-worker-sync",
+    IDS_FLAGS_ENABLE_SERVICE_WORKER_SYNC_NAME,
+    IDS_FLAGS_ENABLE_SERVICE_WORKER_SYNC_DESCRIPTION,
+    kOsAll,
+    SINGLE_VALUE_TYPE(switches::kEnableServiceWorkerSync)
+  },
 #if defined(OS_ANDROID)
   {
     "disable-click-delay",