bookmarks: Move BookmarkNode into 'bookmarks' namespace.

BUG=370433
TEST=unit_tests, components_unittests
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Review URL: https://codereview.chromium.org/865163003

Cr-Commit-Position: refs/heads/master@{#314653}
diff --git a/components/enhanced_bookmarks/metadata_accessor.cc b/components/enhanced_bookmarks/metadata_accessor.cc
index d259832..40c5de9e 100644
--- a/components/enhanced_bookmarks/metadata_accessor.cc
+++ b/components/enhanced_bookmarks/metadata_accessor.cc
@@ -14,6 +14,7 @@
 
 using namespace image::collections;
 using bookmarks::BookmarkModel;
+using bookmarks::BookmarkNode;
 
 namespace {