fixes #27586, prefer context type in generic inference

pkg/dev_compiler/test/codegen_expected/map_keys.js

Index: pkg/dev_compiler/test/codegen_expected/map_keys.js
diff --git a/pkg/dev_compiler/test/codegen_expected/map_keys.js b/pkg/dev_compiler/test/codegen_expected/map_keys.js
index 4f7dcee3f703a6ca0282e5dbe1bc8778086f81a3..f2619017fb18e0428d163d19cb496d459877ac70 100644
--- a/pkg/dev_compiler/test/codegen_expected/map_keys.js
+++ b/pkg/dev_compiler/test/codegen_expected/map_keys.js
@@ -7,12 +7,12 @@ define(['dart_sdk'], function(dart_sdk) {
   const map_keys = Object.create(null);
   let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
   map_keys.main = function() {
-    core.print(dart.map({'1': 2, '3': 4, '5': 6}, core.String, core.int));
-    core.print(dart.map([1, 2, 3, 4, 5, 6], core.int, core.int));
-    core.print(dart.map({'1': 2, [dart.str`${dart.notNull(math.Random.new().nextInt(2)) + 2}`]: 4, '5': 6}, core.String, core.int));
+    core.print(dart.map({'1': 2, '3': 4, '5': 6}));
+    core.print(dart.map([1, 2, 3, 4, 5, 6]));
+    core.print(dart.map({'1': 2, [dart.str`${dart.notNull(math.Random.new().nextInt(2)) + 2}`]: 4, '5': 6}));
     let x = '3';
-    core.print(dart.map(['1', 2, x, 4, '5', 6], core.String, core.int));
-    core.print(dart.map(['1', 2, null, 4, '5', 6], core.String, core.int));
+    core.print(dart.map(['1', 2, x, 4, '5', 6]));
+    core.print(dart.map(['1', 2, null, 4, '5', 6]));
   };
   dart.fn(map_keys.main, VoidTodynamic());
   // Exports: