Hide ARC VPN behind a feature flag

The UI work will be completed in the M64 timeframe, so for M63 we
will require ARC VPN to be manually enabled via chrome://flags#arc-vpn

BUG=696865
TEST=manually test in both Enabled and Disabled state

Change-Id: I5e362f2437629980c69dcfcef60a11786131e986
Reviewed-on: https://chromium-review.googlesource.com/736817
Commit-Queue: Kevin Cernekee <[email protected]>
Reviewed-by: Elijah Taylor <[email protected]>
Reviewed-by: Steven Bennetts <[email protected]>
Cr-Commit-Position: refs/heads/master@{#511507}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index dd63ac6..eba22bb 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2349,6 +2349,10 @@
 const char kArcNativeBridgeExperimentDescription[] =
     "Enables experimental native bridge feature.";
 
+const char kArcVpnName[] = "Enable ARC VPN integration";
+const char kArcVpnDescription[] =
+    "Allow Android VPN clients to tunnel Chrome traffic.";
+
 const char kAshEnableUnifiedDesktopName[] = "Unified desktop mode";
 const char kAshEnableUnifiedDesktopDescription[] =
     "Enable unified desktop mode which allows a window to span multiple "