Add a strong mode implementation of LUB to fasta; use it to infer ?:

pkg/front_end/test/fasta/compile.status

 # Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE.md file.
 
 # Status file for the compile_test.dart (notice c, not k) test suite. This is
 # testing generating Kernel ASTs directly, that is, code in
 # pkg/fasta/lib/src/kernel/.
 
 DeltaBlue: Fail # Missing types on constructor parameters.
 async_function: Fail # Async transformer should be optional.
 await: Fail
 call: Fail # Test can't run.
 covariant_generic: Fail # Missing types on constructor parameters.
 cycles: Fail # Compile-time error handling destroys program.
 external: Fail # External method marked abstract.
 fallthrough: Fail # Missing FallThroughError.
 function_type_recovery: Fail
 invocations: Fail
 micro: Fail # External method marked abstract.
 named_parameters: Fail # Missing types and unnecessary default values.
 optional: Fail # Unnecessary default values.
 redirecting_factory: Fail # Missing types on constructor parameters.
 statements: Fail # Make async tranformer optional for golden file testing.
 type_variable_as_super: Fail
 uninitialized_fields: Fail # Missing types and unnecessary default values.
 void-methods: Fail # Bad return from setters.
 
 inference/*: Fail
+inference/conditional_lub: Pass

[ahe, 2017/05/02 18:32:56]

I think this test is now marked flaky. You probably need to list all the tests
except conditional_lub.

[Paul Berry, 2017/05/03 17:31:25]

Thanks.  Konstantin took care of this in a CL that landed before mine.

 inference/int_upwards_local: Pass
 inference/local_constructor_from_arguments: Pass
 inference/local_reference_upwards_local: Pass
 inference/toplevel_inference_toplevel_var: Pass
 inference/type_promotion_simple: Pass
 inference/type_promotion_stopped_by_access_in_a_closure: Pass
 inference/type_promotion_stopped_by_assignment_in_scope: Pass
 inference/type_promotion_stopped_by_mutation_in_a_closure: Pass
 
 rasta/abstract_constructor: Fail
@@ skipping 50 matching lines @@
 rasta/switch_fall_through: Fail
 rasta/try_label: Fail
 rasta/type_literals: VerificationError
 rasta/type_with_parse_error: Fail
 rasta/typedef: VerificationError
 rasta/unresolved: Fail
 rasta/unresolved_constructor: Fail
 rasta/unresolved_for_in: Fail
 rasta/unresolved_recovery: Fail
 rasta/unsupported_platform_library: Fail