[ImportantSites] Added feature for finch & about:flags

This feature will enable an extra dialog in the CBD flow,
where we allow users to exclude domains that we think are
important to them from being cleared. See project here:
http://goto/importantsites

BUG=579763

Review URL: https://codereview.chromium.org/1900233007

Cr-Commit-Position: refs/heads/master@{#388874}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 74fe5ce0..7b89200 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1816,6 +1816,10 @@
      IDS_FLAGS_MEDIA_STYLE_NOTIFICATION_NAME,
      IDS_FLAGS_MEDIA_STYLE_NOTIFICATION_DESCRIPTION, kOsAndroid,
      FEATURE_VALUE_TYPE(chrome::android::kMediaStyleNotification)},
+    {"important-sites-in-cbd",
+     IDS_FLAGS_IMPORTANT_SITES_IN_CBD_NAME,
+     IDS_FLAGS_IMPORTANT_SITES_IN_CBD_DESCRIPTION, kOsAndroid,
+     FEATURE_VALUE_TYPE(chrome::android::kImportantSitesInCBD)},
 #endif
     {"enable-pointer-events",  // FLAGS:RECORD_UMA
       IDS_FLAGS_EXPERIMENTAL_POINTER_EVENT_NAME,