[Files.app] Add a feature flag for filters in Recents.

I'm going to land implementation (prototype: crrev.com/c/2227714) behind
this flag to make it playable/testable on devices.

Bug: 1114721
Test: Ran unit_tests
Change-Id: I1ed7843216436f91c51fafaebf45e86c79b28821
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2346094
Commit-Queue: Noel Gordon <[email protected]>
Reviewed-by: Noel Gordon <[email protected]>
Cr-Commit-Position: refs/heads/master@{#796778}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 4fd808b..699886b 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -2322,6 +2322,9 @@
 extern const char kFilesZipNoNaClName[];
 extern const char kFilesZipNoNaClDescription[];
 
+extern const char kFiltersInRecentsName[];
+extern const char kFiltersInRecentsDescription[];
+
 extern const char kFrameThrottleFpsName[];
 extern const char kFrameThrottleFpsDescription[];
 extern const char kFrameThrottleFpsDefault[];