Allow Lacros to be enabled on Stable channel via Finch config.

This CL does not currently change any configuration. Lacros is still
disabled by default on stable channel.

Bug: 1144323
Change-Id: I99354aa334931c8688d3eb46ef9e6bca1431efb5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518753
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824185}

chrome/browser/chromeos/crosapi/browser_util.cc

@@ -8,6 +8,7 @@
 
 #include "base/callback.h"
 #include "base/containers/flat_map.h"
+#include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/path_service.h"
 #include "base/process/process_handle.h"
@@ -40,6 +41,10 @@ namespace crosapi {
 namespace browser_util {
 namespace {
 
+// When this feature is enabled, Lacros will be available on stable channel.
+const base::Feature kLacrosAllowOnStableChannel{
+    "LacrosAllowOnStableChannel", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Some account types require features that aren't yet supported by lacros.
 // See https://crbug.com/1080693
 bool IsUserTypeAllowed(const User* user) {
@@ -131,7 +136,7 @@ bool IsLacrosAllowed(Channel channel) {
       // Developer builds can use lacros.
       return true;
     case Channel::STABLE:
-      return false;
+      return base::FeatureList::IsEnabled(kLacrosAllowOnStableChannel);
   }
 }