What should the first line of an error stack trace be, in different scenarios?

gistfile1.js

// scenario 1
var error = new Error('foo');
error.stack; // first line = ?

// scenario 2
var error = new Error('foo');
error.message = 'bar';
error.stack; // first line = ?

// scenario 3
var error = new Error('foo');
error.stack;
error.message = 'bar';
error.stack; // first line = ?

// scenario 4
var error = new Error('foo');
error.message = 'bar';
try {
  throw error;
}
catch (error) {
  error.stack; // first line = ?
}

// scenario 5
var error = new Error('foo');
try {
  throw error;
}
catch (error) {
  error.message = 'bar';
  error.stack; // first line = ?
}

// scenario 6
function BarError() {
  Error.apply(this, arguments);
  this.message = 'bar';
}
BarError.prototype = new Error();
BarError.prototype.name = 'BarError';
BarError.prototype.constructor = BarError;
var error = new BarError();
try {
  throw error;
}
catch (error) {
  error.stack; // first line = ?
}

// scenario 7
function BarError() {
  Error.apply(this, arguments);
  this.message = 'bar';
}
BarError.prototype = Object.create(Error.prototype);
BarError.prototype.name = 'BarError';
BarError.prototype.constructor = BarError;
var error = new BarError();
try {
  throw error;
}
catch (error) {
  error.stack; // first line = ?
}

IE 11—

1. undefined
2. undefined
3. undefined
4. Error: bar
5. Error: bar
6. BarError: bar
7. BarError: bar

Old V8 (Node.js 0.10)—

1. Error: foo
2. Error: bar
3. Error: foo
4. Error: bar
5. Error: bar
6. BarError
7. undefined

New V8 (Node.js master, Chrome 36, Opera 24)—

1. Error: foo
2. Error: foo
3. Error: foo
4. Error: foo
5. Error: foo
6. Error
7. undefined

Firefox 32—

1. first frame of stack
2. first frame of stack
3. first frame of stack
4. first frame of stack
5. first frame of stack
6. first frame of stack
7. empty string

Safari 7.0.6—

1. undefined
2. undefined
3. undefined
4. first frame of stack
5. first frame of stack
6. first frame of stack
7. first frame of stack