[CrOS Cellular] Create feature flag to allow per-network roaming.

This change adds a feature flag that will be used to enable and disable
all future changes related to the migration towards per-network
cellular roaming configuration.

Bug: 1220691
Test: N/A.
Change-Id: Ibfd79e6b0cd72f7f8f02aeec1223204d816a983d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2973394
Commit-Queue: Chad Duffin <[email protected]>
Reviewed-by: Kyle Horimoto <[email protected]>
Cr-Commit-Position: refs/heads/master@{#894940}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index ee6dc34..f8e3b44 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -4077,6 +4077,12 @@
 const char kCdmFactoryDaemonDescription[] =
     "Use the CDM daemon instead of the library CDM";
 
+const char kCellularAllowPerNetworkRoamingName[] =
+    "Allow per-networking roaming";
+const char kCellularAllowPerNetworkRoamingDescription[] =
+    "Allows per-network cellular roaming configuration when cellular roaming "
+    "is not disabled for the device through enterprise policy.";
+
 const char kCellularForbidAttachApnName[] = "Forbid Use Attach APN";
 const char kCellularForbidAttachApnDescription[] =
     "If enabled, the value of |kCellularUseAttachApn| should have no effect "