Add non-null types list to StrongModeOptions

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

Index: pkg/analyzer/test/src/task/strong/non_null_checker_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/non_null_checker_test.dart b/pkg/analyzer/test/src/task/strong/non_null_checker_test.dart
index 1b2a7a6de77f6e864c07d9e3ce6365c4a12c8290..1ba4aaf59baac9fe0ceecc7302677165f71d70ca 100644
--- a/pkg/analyzer/test/src/task/strong/non_null_checker_test.dart
+++ b/pkg/analyzer/test/src/task/strong/non_null_checker_test.dart
@@ -42,4 +42,17 @@ main() {
 }
 ''');
   }
+
+  void test_nullableTypes() {
+    // By default x can be set to null.
+    addFile('''int x = null;''');
+    check();
+  }
+
+  @failingTest
+  void test_nonnullableTypes() {
+    // If `int`s are non-nullable, then this code should throw an error.
+    addFile('''int x = /*error:INVALID_ASSIGNMENT*/null;''');
+    check(nonnullableTypes: <String>['int']);

[Jennifer Messerly, 2016/08/02 16:18:51]

to build on Brian's comment, consider qualifying it with an import URI, e.g.
'dart:core,int'

[Brian Wilkerson, 2016/08/02 16:25:18]

Unless this is intended to be a general purpose mechanism (I want to be able to
declare that my 'Point' class can never be null) that seems like overkill. I was
guessing that this is just to allow the translator to not have to wrap instances
of classes that could otherwise be converted to Java primitive types. But I
probably don't have the full picture, so your call.

[stanm, 2016/08/02 16:56:05]

I agree it's a bit of an overkill, but it actually makes implementing this
experimental feature easier (after adding the import URI, as John mentioned),
since then I can directly do a `contains` check whenever I need to handle
non-nullable types in a special way.

Also, I don't plan to make this user-visible: the actual compiler option will be
something like '--non-nullable-primitives' and will enable a preset collection
of non-nullable classes.

Also, I will add to the commit message that this CL is based on previous work
from Vijay:
https://github.com/dart-lang/dev_compiler/commit/9e124ba8d47963eb378d757ed54d...

(ironically, this is the commit that undoes it : )

+  }
 }