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

test/mjsunit/debug-multiple-var-decl.js

+// Copyright 2016 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
+
+// Test we break at every assignment in a var-statement with multiple
+// variable declarations.
+
+var exception = null;
+var log = []
+
+function f() {
+  var l1 = 1,    // l
+      l2,        // m
+      l3 = 3;    // n
+  let l4,        // o
+      l5 = 5,    // p
+      l6 = 6;    // q
+  const l7 = 7,  // r
+        l8 = 8,  // s
+        l9 = 9;  // t
+  return 0;      // u
+}                // v
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    var line = exec_state.frame(0).sourceLineText();
+    var col = exec_state.frame(0).sourceColumn();
+    print(line);
+    var match = line.match(/\/\/ (\w)$/);
+    assertEquals(2, match.length);
+    log.push(match[1] + col);
+    if (match[1] != "v") {
+      exec_state.prepareStep(Debug.StepAction.StepIn);
+    }
+  } catch (e) {
+    exception = e;
+  }
+}
+
+var Debug = debug.Debug;
+Debug.setListener(listener);
+
+debugger;        // a
+var g1 = 1,      // b
+    g2 = 2,      // c
+    g3;          // d
+let g4 = 4,      // e
+    g5,          // f
+    g6 = 6;      // g
+const g7 = 7,    // h
+      g8 = 8,    // i
+      g9 = f();  // j
+
+Debug.setListener(null);
+
+assertNull(exception);
+
+// Note that let declarations, if not explicitly initialized, implicitly
+// initialize to undefined.
+
+var expected = [
+  "a0",               // debugger statement
+  "b9","c9",          // global var
+  "e9","f4","g9",     // global let
+  "h11","i11","j11",  // global const
+  "l11","n11",        // local var
+  "o6","p11","q11",   // local let
+  "r13","s13","t13",  // local const
+  "u2","v0",          // return
+];
+assertEquals(expected, log);