Fix a type error that occurs comparing two large maps with deepEquals.

pkgs/checks/lib/src/describe.dart

@@ -72,7 +72,11 @@ Iterable<String> _prettyPrint(
 Iterable<String> _prettyPrintCollection(
     String open, String close, List<Iterable<String>> elements, int maxLength) {
   if (elements.length > _maxItems) {
-    elements.replaceRange(_maxItems - 1, elements.length, [
+    // Force inference as List<String>, otherwise the type is
+    // List<Iterable<String>> which ends up as a type error in dart:collection
+    // when the underlying list is actually a List<List<String>>. See
+    // https://github.com/dart-lang/test/issues/2441 for more details.
+    elements.replaceRange(_maxItems - 1, elements.length, <List<String>>[
       ['...']
     ]);
   }

pkgs/checks/test/extensions/map_test.dart

@@ -29,6 +29,65 @@ void main() {
   test('values', () {
     check(_testMap).values.contains(1);
   });
+  test('can be described failing compared to another large map', () {
+    const expected = {
+      1: -5,
+      2: -4,
+      3: -4,
+      4: -3,
+      5: -3,
+      6: -2,
+      7: -2,
+      8: -1,
+      9: -1,
+      10: 0,
+      11: 0,
+      12: 1,
+      13: 1,
+      14: 2,
+      15: 2,
+      16: 3,
+      17: 3,
+      18: 4,
+      19: 4,
+      20: 5,
+      21: 5,
+      22: 6,
+      23: 6,
+      24: 7,
+      25: 7,
+      26: 8,
+    };
+    final actual = {
+      1: -4,
+      2: -4,
+      3: -3,
+      4: -3,
+      5: -2,
+      6: -2,
+      7: -1,
+      8: -1,
+      9: 0,
+      10: 0,
+      11: 0,
+      12: 1,
+      13: 1,
+      14: 2,
+      15: 2,
+      16: 3,
+      17: 3,
+      18: 4,
+      19: 4,
+      20: 5,
+      21: 5,
+      22: 6,
+      23: 6,
+      24: 7,
+      25: 7,
+      26: 8,
+    };
+    check(actual).not((a) => a.deepEquals(expected));
+  });
 
   group('operator []', () {
     test('succeeds for a key that exists', () {