fixes #27586, prefer context type in generic inference

pkg/dev_compiler/lib/src/compiler/code_generator.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.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 5499 matching lines @@
     // TODO(jmesserly): verify this is unreachable.
     throw 'Unimplemented ${node.runtimeType}: $node';
   }
 
   _visit(AstNode node) {
     if (node == null) return null;
     var result = node.accept(this);
     return result is JS.Node ? annotate(result, node) : result;
   }
 
-  List/*<T>*/ _visitList/*<T extends AstNode>*/(Iterable/*<T>*/ nodes) {
+  // TODO(jmesserly): we should make sure this only returns JS AST nodes.
+  List/*<R>*/ _visitList/*<T extends AstNode, R>*/(Iterable/*<T>*/ nodes) {
     if (nodes == null) return null;
-    var result = /*<T>*/ [];
-    for (var node in nodes) result.add(_visit(node) as dynamic/*=T*/);
+    var result = /*<R>*/ [];
+    for (var node in nodes) result.add(_visit(node) as dynamic/*=R*/);
     return result;
   }
 
   /// Visits a list of expressions, creating a comma expression if needed in JS.
   JS.Expression _visitListToBinary(List<Expression> nodes, String operator) {
     if (nodes == null || nodes.isEmpty) return null;
     return new JS.Expression.binary(
         _visitList(nodes) as List<JS.Expression>, operator);
   }
 
@@ skipping 483 matching lines @@
   if (targetIdentifier.staticElement is! PrefixElement) return false;
   var prefix = targetIdentifier.staticElement as PrefixElement;
 
   // The library the prefix is referring to must come from a deferred import.
   var containingLibrary = resolutionMap
       .elementDeclaredByCompilationUnit(target.root as CompilationUnit)
       .library;
   var imports = containingLibrary.getImportsWithPrefix(prefix);
   return imports.length == 1 && imports[0].isDeferred;
 }