[CrOS MultiDevice] Add flag for Messages staging URL.

When this flag is enabled, the staging URL will be used instead of the
production URL. A follow-up CL will actually use this flag.

Bug: 917855
Change-Id: Ia8d266caefa8abe2e44f293e7c63c2c214b21491
Reviewed-on: https://chromium-review.googlesource.com/c/1447025
Reviewed-by: Avi Drissman <[email protected]>
Reviewed-by: Jeremy Klein <[email protected]>
Commit-Queue: Kyle Horimoto <[email protected]>
Cr-Commit-Position: refs/heads/master@{#627698}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 90d764bf..610017f 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1517,6 +1517,9 @@
      flag_descriptions::kUseMessagesGoogleComDomainName,
      flag_descriptions::kUseMessagesGoogleComDomainDescription, kOsCrOS,
      FEATURE_VALUE_TYPE(chromeos::features::kUseMessagesGoogleComDomain)},
+    {"use_messages_staging_url", flag_descriptions::kUseMessagesStagingUrlName,
+     flag_descriptions::kUseMessagesStagingUrlDescription, kOsCrOS,
+     FEATURE_VALUE_TYPE(chromeos::features::kUseMessagesStagingUrl)},
     {"enable_messages_web_push", flag_descriptions::kEnableMessagesWebPushName,
      flag_descriptions::kEnableMessagesWebPushDescription, kOsCrOS,
      FEATURE_VALUE_TYPE(chromeos::features::kEnableMessagesWebPush)},