test, first pass at a fix

src/compiler/checker.ts

@@ -200,6 +200,10 @@ namespace ts {
             "symbol": {
                 type: esSymbolType,
                 flags: TypeFlags.ESSymbol
+            },
+            "undefined": {
+                type: undefinedType,
+                flags: TypeFlags.ContainsUndefinedOrNull
             }
         };
 

tests/cases/conformance/expressions/typeGuards/typeGuardTypeOfUndefined.ts

@@ -0,0 +1,28 @@
+// undefined type guard adds no new type information
+function test1(a: any) {
+    if (typeof a !== "undefined") {
+        if (typeof a === "boolean") {
+            a;
+        }
+    }
+}
+
+function test2(a: any) {
+    if (typeof a === "undefined") {
+        if (typeof a === "boolean") {
+            a;
+        }
+    }
+}
+
+function test3(a: any) {
+    if (typeof a === "undefined" || typeof a === "boolean") {
+		a;
+    }
+}
+
+function test4(a: any) {
+    if (typeof a !== "undefined" && typeof a === "boolean") {
+		a;
+    }
+}