[merge addon] Lazily initialize diff_match_patch

Author: scipper

addon/merge/merge.js

@@ -644,9 +644,10 @@
   }
 
   // Operations on diffs
-
-  var dmp = new diff_match_patch();
+  var dmp;
   function getDiff(a, b, ignoreWhitespace) {
+    if (!dmp) dmp = new diff_match_patch();
+
     var diff = dmp.diff_main(a, b);
     // The library sometimes leaves in empty parts, which confuse the algorithm
     for (var i = 0; i < diff.length; ++i) {