Add/fix/cleanup type inference for throw and rethrow.

pkg/front_end/testcases/kompile.status

Index: pkg/front_end/testcases/kompile.status
diff --git a/pkg/front_end/testcases/kompile.status b/pkg/front_end/testcases/kompile.status
index 3f3e3bee33a51d1ae0c7b038092f35e1e5f30c9d..a26c0ba85340bbf5d7ac99038000dd9a6f9d6574 100644
--- a/pkg/front_end/testcases/kompile.status
+++ b/pkg/front_end/testcases/kompile.status
@@ -252,6 +252,7 @@ inference/infer_parameter_type_setter_from_field: Crash
 inference/infer_parameter_type_setter_from_setter: Crash
 inference/infer_prefix_expression: Crash
 inference/infer_prefix_expression_custom: Crash
+inference/infer_rethrow: Crash
 inference/infer_return_of_statement_lambda: Crash
 inference/infer_setter_cross_to_getter: Crash
 inference/infer_setter_from_later_inferred_setter: Crash
@@ -266,6 +267,7 @@ inference/infer_statics_transitively_b: Crash
 inference/infer_statics_with_method_invocations: Crash
 inference/infer_statics_with_method_invocations_a: Crash
 inference/infer_throw: Crash
+inference/infer_throw_downwards: Crash
 inference/infer_type_on_overridden_fields2: Crash
 inference/infer_type_on_overridden_fields4: Crash
 inference/infer_type_on_var_from_field: Crash