Incorrect constructor renaming when factory class implements the interface

[ghost]

language tests: FactoryImplementationTest.dart

interface A factory B {
  A(int x, int y);
}

// new A() invokes B constructor because B implements A.
class B implements A {
  final int x;
  final int y;

  B(this.x, this.y);
  
// This factory will never be invoked.
  factory A(int a, int b) { return new B(0, 0); }

}

[anders-sandholm]

Removed Area-Frog label.
Added Area-Dart2JS, FromAreaFrog labels.

[kasperl]

Added WontFix label.