Fix break location calculation.

test/mjsunit/regress/regress-419663.js

+// Copyright 2012 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
+
+var o = {
+  f: function(x) {
+    var a = x + 1;
+    o = 1;
+  }
+}
+
+function sentinel() {}
+
+var Debug = debug.Debug;
+
+Debug.setListener(function() {});
+
+var script = Debug.findScript(sentinel);
+
+// Used in Debug.setScriptBreakPointById.
+var p1 = Debug.findScriptSourcePosition(script, 9, 0);
+var p2 = Debug.setBreakPointByScriptIdAndPosition(script.id, p1).actual_position;
+var p3 = Debug.setBreakPointByScriptIdAndPosition(script.id, p2).actual_position;
+
+assertEquals(p2, p3);
+
+function assertLocation(p, l, c) {
+  var location = script.locationFromPosition(p, false);
+  assertEquals(l, location.line);
+  assertEquals(c, location.column);
+}
+
+assertLocation(p1, 9, 0);
+assertLocation(p2, 9, 4);
+assertLocation(p3, 9, 4);