Initial CL for Data Saver (Flywheel) prompt when cellular network detected

chromeos/chromeos_switches.cc

Index: chromeos/chromeos_switches.cc
diff --git a/chromeos/chromeos_switches.cc b/chromeos/chromeos_switches.cc
index 3c945b1d12d1a1e78a529b028f39d50b02c79dca..95e8c3dae2dae102fd5a191ca6f284d681e03129 100644
--- a/chromeos/chromeos_switches.cc
+++ b/chromeos/chromeos_switches.cc
@@ -322,6 +322,9 @@ const char kEnableCaptivePortalBypassProxy[] =
 const char kDisableTimeZoneTrackingOption[] =
     "disable-timezone-tracking-option";
 
+// Enable Data Saver prompt on 3G networks.
+const char kEnableDataSaverPrompt[] = "enable-datasaver-prompt";
+
 bool WakeOnWifiEnabled() {
   return !base::CommandLine::ForCurrentProcess()->HasSwitch(kDisableWakeOnWifi);
 }