Added a SyncClipboardService.

This is mostly an observer of a synced pref, that puts its contents on
the clipboard whenever it changes.

This feature is currently behind a feature flag and is disabled by
default.

Change-Id: Id038cd2190cbdb1c1c20b567933274715018cc0e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1781442
Reviewed-by: David Roger <[email protected]>
Reviewed-by: Mike West <[email protected]>
Reviewed-by: Mikel Astiz <[email protected]>
Commit-Queue: Joao da Silva <[email protected]>
Cr-Commit-Position: refs/heads/master@{#693212}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index a689ee7..73dbde6 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -4499,6 +4499,12 @@
      FEATURE_VALUE_TYPE(content_settings::kImprovedCookieControls)},
 #endif  // !defined(OS_ANDROID)
 
+#if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX)
+    {"sync-clipboard-service", flag_descriptions::kSyncClipboardServiceName,
+     flag_descriptions::kSyncClipboardServiceDescription, kOsDesktop,
+     FEATURE_VALUE_TYPE(features::kSyncClipboardServiceFeature)},
+#endif  // OS_WIN || OS_MACOSX || OS_LINUX
+
     // NOTE: Adding a new flag requires adding a corresponding entry to enum
     // "LoginCustomFlags" in tools/metrics/histograms/enums.xml. See "Flag
     // Histograms" in tools/metrics/histograms/README.md (run the