Generalize the first argument in an assert to be an expression (issue 26865)

tests/language/language_analyzer2.status

 # Copyright (c) 2012, 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 file.
 
 [ $compiler == dart2analyzer ]
 
 regress_26668_test: Fail # Issue 26678
 regress_26855_test/4: Fail # Issue 26860
 
 # Runtime negative test. No static errors or warnings.
@@ skipping 106 matching lines @@
 # test issue 12161, type variable in static, malformed type, static warning
 type_variable_static_context_negative_test: fail
 
 # test issue 12163, unresolved identifier is static warning in static context
 unresolved_in_factory_negative_test: fail # Issue 12163
 unresolved_top_level_var_negative_test: fail # Issue 12163
 
 # test issue 12191, ambiguous import is always warning now
 prefix3_negative_test: fail # Issue 12191
 
-# test issue 12289, assignment in assert statement
-type_error_test: fail # Issue 12289
-
 # test issue 12381, It is compile-time error to invoke not existing function
 issue11724_test: fail # Issue 12381
 
 # test issue 12541; there shouldn't be a static warning
 static_field_test/01: fail # Issue 12541
 static_field_test/02: fail # Issue 12541
 static_field_test/03: fail # Issue 12541
 static_field_test/04: fail # Issue 12541
 
 # test issue 13916, Looks as no warning should be in this redirecting factory
@@ skipping 369 matching lines @@
 generic_methods_new_test: CompiletimeError # Issue 25868
 generic_methods_function_type_test: CompiletimeError # Issue 25868
 generic_methods_type_expression_test: CompiletimeError # Issue 25868
 
 # Experimental feature: Use initializing formals in initializers and constructor body.
 initializing_formal_access_test: CompiletimeError # Issue 26658
 initializing_formal_capture_test: CompiletimeError # Issue 26658
 initializing_formal_final_test: CompiletimeError # Issue 26658
 initializing_formal_promotion_test: StaticWarning # Issue 26658
 initializing_formal_type_test: CompiletimeError # Issue 26658