[Experiment] Replace sync for favicons with request to LargeIconService

For history webuis and the recent tabs menu, we offer the possibility
of using requests to Google's favicon server as a fallback mechanism,
instead of requesting from sync. We use LargeIconService to achieve it.
This behavior is guarded by a feature flag disabled by default. We also
fix a minor formatting issue in chrome/browser/about_flags.cc.

Bug: 955475
Change-Id: I1ff64611cfde1e995a14b36ea2496b33d214eea2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1603444
Commit-Queue: Victor Vianna <[email protected]>
Reviewed-by: Nicolas Ouellet-Payeur <[email protected]>
Reviewed-by: Mikel Astiz <[email protected]>
Reviewed-by: Peter Kasting <[email protected]>
Reviewed-by: Esmael El-Moslimany <[email protected]>
Reviewed-by: Jan Krcal <[email protected]>
Cr-Commit-Position: refs/heads/master@{#662205}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index dcb8162..af61066 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -359,6 +359,9 @@
 extern const char kEnableGpuServiceLoggingName[];
 extern const char kEnableGpuServiceLoggingDescription[];
 
+extern const char kEnableHistoryFaviconsGoogleServerQueryName[];
+extern const char kEnableHistoryFaviconsGoogleServerQueryDescription[];
+
 extern const char kEnableImplicitRootScrollerName[];
 extern const char kEnableImplicitRootScrollerDescription[];