noImplicitAny+prototype assignment causes incorrect error on prototype methods

[sandersn]

Note that this is only true with noImplicitAny on. The bug does not manifest with it off.
This is a regression in 3.1. It does not manifest in 3.0.

// @noImplicitAny: true
/** @constructor */
var Multimap = function() {
    this._map = {};
};

Multimap.prototype = {
  x() { }
}

Multimap.prototype.lol = function() {
}

var mm = new Multimap();
mm._map
mm.x
mm.lol

Expected behavior:
No error on Multimap.prototype.lol, and _map, x and lol are properties on Multimap.

Actual behavior:
Error: 'lol' does not exist on type '{ x(): void }'. But all 3 are properties on Multimap.

[sandersn]

The solution might be to better understand prototype assignment in getWidenedTypeFromJSPropertyAssignments. I tried calling getJavascriptClassType when there's a prototype assignment, but that resulted in a circularity. Probably a slightly more complex fix will work.

[sandersn]

This is now fixed.

Edit: Nope, I read expected/actual backward.