[sync] Componentize switches used by ProfileSyncService

This CL componentizes switches used by ProfileSyncService and
ProfileSyncComponentsFactoryImpl into a new browser_sync component in
anticipation of componentizing those files into that component.

These switches are used by //cloud_print/service, and so are componentized into
//components/browser_sync/common to allow for that dependency without
//cloud_print/service incurring a dependency on the browser-side code (e.g.,
ProfileSyncService) once that code is componentized.

BUG=512825
TBR=jochen

Review URL: https://codereview.chromium.org/1408003010

Cr-Commit-Position: refs/heads/master@{#358048}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 37fbb00..7cba4ca 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -103,6 +103,7 @@
     "//components/autofill/core/browser",
     "//components/bookmarks/browser",
     "//components/bookmarks/managed",
+    "//components/browser_sync/common",
     "//components/captive_portal",
     "//components/certificate_reporting",
     "//components/cloud_devices/common",