Componentize bookmark-related sync files into new component

This CL componentizes files related to syncing of bookmarks into a new
sync_bookmarks component. The motivation is for clean iOS integration. The files
have no problematic dependencies and so can be componentized as-is.

The decision to create a standalone component rather than folding these files
into the bookmarks component is that it is undesirable to introduce a
sync-related dependency in the core bookmark component.

BUG=511299,511293,511287
TBR=thestig

Review URL: https://codereview.chromium.org/1395563002

Cr-Commit-Position: refs/heads/master@{#353065}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 783d064b..33b567c 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -155,6 +155,7 @@
     "//components/startup_metric_utils",
     "//components/strings",
     "//components/suggestions",
+    "//components/sync_bookmarks",
     "//components/sync_driver",
     "//components/tracing:startup_tracing",
     "//components/translate/core/browser",