Add feature flag for descriptive failed offline page status text

Check flag when determining status text for a failed download attempt.
When the flag is enabled, descriptive status texts should be used for
downloads that failed due to an actionable error. Descriptive status
texts still are TBD. When the flag is disabled, use generic "Download
failed."

Bug: 824931
Change-Id: I2d67a7c3213a3a57a39b72eeae7433a6b847283e
Reviewed-on: https://chromium-review.googlesource.com/982520
Commit-Queue: Candice Sy <[email protected]>
Reviewed-by: Cathy Li <[email protected]>
Reviewed-by: David Trainor <[email protected]>
Reviewed-by: Joy Ming <[email protected]>
Cr-Commit-Position: refs/heads/master@{#547324}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9785caa..ccd7e2d 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2324,6 +2324,12 @@
      flag_descriptions::kBackgroundLoaderForDownloadsName,
      flag_descriptions::kBackgroundLoaderForDownloadsDescription, kOsAndroid,
      FEATURE_VALUE_TYPE(offline_pages::kBackgroundLoaderForDownloadsFeature)},
+    {"offline-pages-failed-download",
+     flag_descriptions::kOfflinePagesDescriptiveFailStatusName,
+     flag_descriptions::kOfflinePagesDescriptiveFailStatusDescription,
+     kOsAndroid,
+     FEATURE_VALUE_TYPE(
+         offline_pages::kOfflinePagesDescriptiveFailStatusFeature)},
     {"offline-pages-pending-download",
      flag_descriptions::kOfflinePagesDescriptivePendingStatusName,
      flag_descriptions::kOfflinePagesDescriptivePendingStatusDescription,