Add this narrowing test and update previous test

tests/cases/compiler/anonymousClassExpression2.ts

@@ -0,0 +1,17 @@
+// Fixes #14860
+// note: repros with `while (0);` too
+// but it's less inscrutable and more obvious to put it *inside* the loop
+while (0) {
+    class A {
+        methodA() {
+            this; //note: a this reference of some kind is required to trigger the bug
+        }
+    }
+
+    class B {
+        methodB() {
+            this.methodA; // error
+            this.methodB; // ok
+        }
+    }
+}

tests/cases/compiler/narrowedConstInMethod.ts

@@ -1,10 +1,11 @@
 // @strictNullChecks: true
 
+// Fixes #10501, possibly null 'x'
 function f() {
     const x: string | null = <any>{};
     if (x !== null) {
         return {
-            bar() { return x.length; }  // Error: possibly null x
+            bar() { return x.length; }  // ok
         };
     }
 }
@@ -13,7 +14,7 @@ function f2() {
     const x: string | null = <any>{};
     if (x !== null) {
         return class {
-            bar() { return x.length; }  // Error: possibly null x
+            bar() { return x.length; }  // ok
         };
     }
-}
+}