message: applyMixinsWithoutProperties doesn't copy constructor
  Don't copy ES6 constructors while applying mixing to prototype, because
  it messes with class model as mixin constructor appears as class name in
  console.
  Also, who knows what happens if we copy "reserved" property like
  "constructor".
diff: @@ -32,7 +32,11 @@ export function applyMixinsWithoutProperties(derivedCtor: any, baseCtors: any[])
  baseCtors.forEach(baseCtor => {
  Object.getOwnPropertyNames(baseCtor.prototype).forEach(name => {
  const descriptor = Object.getOwnPropertyDescriptor(baseCtor.prototype, name);
  - if (descriptor !== undefined && descriptor.get === undefined) {
  + if (
  + descriptor !== undefined &&
  + descriptor.get === undefined &&
  + name !== "constructor"
  + ) {
  derivedCtor.prototype[name] = baseCtor.prototype[name];
  }
  });
  