Add bookmark entry point histogram for bookmark prompt experiment

chrome/browser/bookmarks/bookmark_utils.h

Index: chrome/browser/bookmarks/bookmark_utils.h
diff --git a/chrome/browser/bookmarks/bookmark_utils.h b/chrome/browser/bookmarks/bookmark_utils.h
index d7f0aee2d46aea5d6f0d62b3351b45ba4597f631..31245c16f741e95ecaecf777d4d57761a405fbdf 100644
--- a/chrome/browser/bookmarks/bookmark_utils.h
+++ b/chrome/browser/bookmarks/bookmark_utils.h
@@ -231,6 +231,16 @@ void RemoveAllBookmarks(BookmarkModel* model, const GURL& url);
 // value.
 extern int num_urls_before_prompting;
 
+// This enum is used for the Bookmarks.EntryPoint histogram.
+enum BoomarkEntryPoint {
+  ENTRY_POINT_ACCELERATOR,
+  ENTRY_POINT_STAR_GESTURE,
+  ENTRY_POINT_STAR_KEY,
+  ENTRY_POINT_STAR_MOUSE,
+
+  ENTRY_POINT_LIMIT // Keep this last.
+};
+
 // This enum is used for the Bookmarks.LaunchLocation histogram.
 enum BookmarkLaunchLocation {
   LAUNCH_NONE,