Add super to control flow.

It is handled the same way as 'this'

Author: sandersn

src/compiler/binder.ts

@@ -703,6 +703,7 @@ namespace ts {
         function isNarrowableReference(expr: Expression): boolean {
             return expr.kind === SyntaxKind.Identifier ||
                 expr.kind === SyntaxKind.ThisKeyword ||
+                expr.kind === SyntaxKind.SuperKeyword ||
                 expr.kind === SyntaxKind.PropertyAccessExpression && isNarrowableReference((<PropertyAccessExpression>expr).expression);
         }
 

src/compiler/checker.ts

@@ -10347,6 +10347,8 @@ namespace ts {
                         getExportSymbolOfValueSymbolIfExported(getResolvedSymbol(<Identifier>source)) === getSymbolOfNode(target);
                 case SyntaxKind.ThisKeyword:
                     return target.kind === SyntaxKind.ThisKeyword;
+                case SyntaxKind.SuperKeyword:
+                    return target.kind === SyntaxKind.SuperKeyword;
                 case SyntaxKind.PropertyAccessExpression:
                     return target.kind === SyntaxKind.PropertyAccessExpression &&
                         (<PropertyAccessExpression>source).name.text === (<PropertyAccessExpression>target).name.text &&
@@ -11483,6 +11485,7 @@ namespace ts {
                 switch (expr.kind) {
                     case SyntaxKind.Identifier:
                     case SyntaxKind.ThisKeyword:
+                    case SyntaxKind.SuperKeyword:
                     case SyntaxKind.PropertyAccessExpression:
                         return narrowTypeByTruthiness(type, expr, assumeTrue);
                     case SyntaxKind.CallExpression: