[debugger] break at each initialization in a multiple var declaration.

test/mjsunit/es6/debug-stepin-string-template.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-debug-as debug
 
 Debug = debug.Debug
 
 var exception = null;
 var log = [];
@@ skipping 30 matching lines @@
 
 Debug.setListener(listener);
 debugger;                                         // a
 var s = `1 ${u("a")} 2 ${u("b")} 3 ${n} 4 ${o}`;  // b
 Debug.setListener(null);                          // c
 
 assertNull(exception);
 
 assertEquals([
   "a0",
-  "b0",
+  "b44",
+  "b13",
   "d2b13",
   "e0b13",
   "b25",
   "d2b25",
   "e0b25",
   "f4b44",
   "g2b44",
   "c0"
 ], log);