Reify implicit casts for FutureOr

pkg/dev_compiler/test/codegen_test.dart

 // 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 file.
 
 /// Tests code generation.
 ///
 /// Runs Dart Dev Compiler on all input in the `codegen` directory and checks
 /// that the output is what we expected.
 library dev_compiler.test.codegen_test;
 
@@ skipping 138 matching lines @@
       var files = new Set<String>();
       _collectTransitiveImports(contents, files, from: testFile);
       var unit = new BuildUnit(
           name, path.dirname(testFile), files.toList(), _moduleForLibrary);
 
       var compiler = sharedCompiler;
       if (analyzerOptions.declaredVariables.isNotEmpty) {
         compiler = new ModuleCompiler(analyzerOptions);
       }
       JSModuleFile module = null;
+      var exception = null;
       try {
         module = compiler.compile(unit, options);
-      } catch (e) {}
+      } catch (e) {
+        exception = e;
+      }
 
       bool expectedCompileTimeError =
           contents.contains(': compile-time error\n');
       bool notStrong = notYetStrongTests.contains(name);
       bool crashing = _crashingTests.contains(name);
 
       if (module == null) {
         expect(crashing, isTrue,
-            reason: "test $name crashes during compilation.");
+            reason: "test $name crashes during compilation:\n $exception");
       } else if (module.isValid) {
         _writeModule(
             path.join(codegenOutputDir, name),
             isTopLevelTest ? path.join(codegenExpectDir, name) : null,
             moduleFormat,
             module);
 
         expect(crashing, isFalse, reason: "test $name no longer crashes.");
         // TODO(vsm): We don't seem to trip on non-strong errors?
         // expect(expectedCompileTimeError, isFalse,
@@ skipping 208 matching lines @@
 
   // TODO(vsm): Fix these - they import files from a different directory
   // - this triggers an invalid library root build error.
   'lib/html/custom/attribute_changed_callback_test',
   'lib/html/custom/constructor_calls_created_synchronously_test',
   'lib/html/custom/entered_left_view_test',
   'lib/html/custom/js_custom_test',
   'lib/html/custom/mirrors_test',
   'lib/html/custom/regress_194523002_test',
 ]);