[Media Feeds] Add about flag entry

Add an about flags entry for Media Feeds.

Also switches the "safe search" feature on
by default which is gated on the main feature
anyway.

BUG=1053599

Change-Id: Ibb2bb98a3a6a55fee23166f3a8acd5510e0949aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2193974
Reviewed-by: Tommy Steimel <[email protected]>
Commit-Queue: Becca Hughes <[email protected]>
Cr-Commit-Position: refs/heads/master@{#767485}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index d6af02a..494a330 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -3916,6 +3916,11 @@
 #if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX) || \
     defined(OS_CHROMEOS)
 
+const char kEnableMediaFeedsName[] = "Enables Media Feeds";
+const char kEnableMediaFeedsDescription[] =
+    "Enables the Media Feeds feature which allows us to fetch feeds of media "
+    "items from websites that support the feature. ";
+
 const char kRemoteCopyReceiverName[] =
     "Enables the remote copy feature to receive messages";
 const char kRemoteCopyReceiverDescription[] =