fix wrong order to isAssignableTo for override params

pkg/analyzer/test/src/task/strong/checker_test.dart

Index: pkg/analyzer/test/src/task/strong/checker_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/checker_test.dart b/pkg/analyzer/test/src/task/strong/checker_test.dart
index 1b4dac99da5acdd8eb3ff7df31a7d5ea58c98748..7d6f844f9398e8806b0e46e0177863b2dd7bb48c 100644
--- a/pkg/analyzer/test/src/task/strong/checker_test.dart
+++ b/pkg/analyzer/test/src/task/strong/checker_test.dart
@@ -3009,6 +3009,23 @@ void takesF(void f(int x)) {
     ''');
   }
 
+  void test_overrideNarrowsType() {
+    addFile(r'''
+class A {}
+class B extends A {}
+
+abstract class C {
+  m(A a);
+  n(B b);
+}
+abstract class D extends C {
+  /*error:INVALID_METHOD_OVERRIDE*/m(/*error:INVALID_METHOD_OVERRIDE_NORMAL_PARAM_TYPE*/B b);

[Jennifer Messerly, 2016/08/10 23:50:48]

we should probably let error_verifier's messages replace ours. it's a bit
confusing right now we do the checking in two places. e.g. for @covariant
overrides I will have to fix both.

+  n(A a);
+}
+    ''');
+    check(implicitCasts: false);

[Jennifer Messerly, 2016/08/10 23:50:48]

This bug wasn't visible until we turn off implicit casts. The reason is we have
our own override checking in checker.dart for strong mode, and isAssignableTo is
highly permissive even in strong mode. So we just didn't see this problem. Same
deal in Dart 1 -- the order (almost) didn't matter.

+  }
+
   void test_privateOverride() {
     addFile(
         '''