Add Apps.AppListSearchResultDistanceFromOrigin UMA stat.

ui/app_list/app_list_constants.cc

Index: ui/app_list/app_list_constants.cc
diff --git a/ui/app_list/app_list_constants.cc b/ui/app_list/app_list_constants.cc
index a3c0ada4bce6a28e5b9723ef8fc23bbaa423ac03..8f62799c21681e0769cd9d3f8dea0bd3348ff663 100644
--- a/ui/app_list/app_list_constants.cc
+++ b/ui/app_list/app_list_constants.cc
@@ -133,6 +133,11 @@ const char kSearchResultOpenDisplayTypeHistogram[] =
 // opened.
 const char kSearchQueryLength[] = "Apps.AppListSearchQueryLength";
 
+// The UMA histogram that logs the Manhattan distance from the origin of the
+// search results to the selected result.
+const char kSearchResultDistanceFromOrigin[] =
+    "Apps.AppListSearchResultDistanceFromOrigin";
+
 #if defined(OS_LINUX)
 #if defined(GOOGLE_CHROME_BUILD)
 const char kAppListWMClass[] = "chrome_app_list";