fixes #27586, prefer context type in generic inference

pkg/analyzer/test/generated/strong_mode_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.
 
 library analyzer.test.generated.strong_mode_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
@@ skipping 1434 matching lines @@
         Expression exp = (statements[i] as ExpressionStatement).expression;
         expect(exp.staticType, typeProvider.dynamicType);
       }
     }
 
     checkBody("C");
     checkBody("D");
   }
 
   void test_genericFunction_upwardsAndDownwards() {
-    // Regression tests for https://github.com/dart-lang/sdk/issues/27151.
+    // Regression tests for https://github.com/dart-lang/sdk/issues/27586.
     resolveTestUnit(r'List<num> x = [1, 2];');
-    expectInitializerType('x', 'List<int>');
+    expectInitializerType('x', 'List<num>');
   }
 
+  void test_genericFunction_upwardsAndDownwards_Object() {

[Leaf, 2016/11/30 05:24:30]

Can you add a version of this using generic methods and one using constructors,
since those go through somewhat different paths in places?

+    // Regression tests for https://github.com/dart-lang/sdk/issues/27625.
+    resolveTestUnit(r'''
+List<Object> aaa = [];
+List<Object> bbb = [1, 2, 3];
+List<Object> ccc = [null];
+List<Object> ddd = [1 as dynamic];
+List<Object> eee = [new Object()];

[Leaf, 2016/11/30 05:24:29]

Do we have any test cases for inference which uses the new partial contexts?

+    ''');
+    expectInitializerType('aaa', 'List<Object>');
+    expectInitializerType('bbb', 'List<Object>');
+    expectInitializerType('ccc', 'List<Object>');
+    expectInitializerType('ddd', 'List<Object>');
+    expectInitializerType('eee', 'List<Object>');
+  }
+
+
   void test_genericMethod() {
     resolveTestUnit(r'''
 class C<E> {
   List/*<T>*/ f/*<T>*/(E e) => null;
 }
 main() {
   C<String> cOfString;
 }
 ''');
     expectFunctionType('f', '<T>(E) → List<T>',
@@ skipping 931 matching lines @@
 main() {
   var v = x;
   v; // marker
 }
 int x = 3;
 ''';
     assertPropagatedAssignedType(code, typeProvider.intType, null);
     assertTypeOfMarkedExpression(code, typeProvider.intType, null);
   }
 }