fix #25487, infer block lambdas from return statements

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

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 library analyzer.test.src.task.strong.strong_test_helper;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 34 matching lines @@
 void addFile(String content, {String name: '/main.dart'}) {
   name = name.replaceFirst('^package:', '/packages/');
   files.newFile(name, content);
 }
 
 /// Run the checker on a program, staring from '/main.dart', and verifies that
 /// errors/warnings/hints match the expected value.
 ///
 /// See [addFile] for more information about how to encode expectations in
 /// the file text.
-void check() {
+///
+/// Returns the main resolved library. This can be used for further checks.
+CompilationUnit check() {
   _checkCalled = true;
 
   expect(files.getFile('/main.dart').exists, true,
       reason: '`/main.dart` is missing');
 
   var uriResolver = new _TestUriResolver(files);
   // Enable task model strong mode
   var context = AnalysisEngine.instance.createAnalysisContext();
   context.analysisOptions.strongMode = true;
   (context.analysisOptions as AnalysisOptionsImpl).strongModeHints = true;
@@ skipping 20 matching lines @@
       var librarySource = context.getLibrariesContaining(source).single;
       var resolved = context.resolveCompilationUnit2(source, librarySource);
       errors.addAll(context.getErrors(source).errors.where((e) =>
           e.errorCode != HintCode.UNUSED_LOCAL_VARIABLE &&
           // TODO(jmesserly): these are usually intentional dynamic calls.
           e.errorCode.name != 'UNDEFINED_METHOD'));
 
       _expectErrors(resolved, errors);
     }
   }
+
+  return initialLibrary;
 }
 
 /// Adds a file using [addFile] and calls [check].
-void checkFile(String content) {
+///
+/// Also returns the resolved compilation unit.
+CompilationUnit checkFile(String content) {
   addFile(content);
-  check();
+  return check();
 }
 
 SourceSpanWithContext _createSpanHelper(
     LineInfo lineInfo, int start, Source source, String content,
     {int end}) {
   var startLoc = _locationForOffset(lineInfo, source.uri, start);
   var endLoc = _locationForOffset(lineInfo, source.uri, end ?? start);
 
   var lineStart = startLoc.offset - startLoc.column;
   // Find the end of the line. This is not exposed directly on LineInfo, but
@@ skipping 266 matching lines @@
 
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     if (uri.scheme == 'package') {
       return (provider.getResource('/packages/' + uri.path) as File)
           .createSource(uri);
     }
     return super.resolveAbsolute(uri, actualUri);
   }
 }