Fix newly introduced errors and warnings

pkg/analyzer/test/src/task/dart_work_manager_test.dart

Index: pkg/analyzer/test/src/task/dart_work_manager_test.dart
diff --git a/pkg/analyzer/test/src/task/dart_work_manager_test.dart b/pkg/analyzer/test/src/task/dart_work_manager_test.dart
index 84f3f6332cc5db2ad431c0aa8d9ec73da58beefa..12388d086ccf26360bd2272d085eaf6cadfe95b5 100644
--- a/pkg/analyzer/test/src/task/dart_work_manager_test.dart
+++ b/pkg/analyzer/test/src/task/dart_work_manager_test.dart
@@ -357,11 +357,13 @@ class DartWorkManagerTest {
     when(context.aboutToComputeResult(anyObject, CONTAINING_LIBRARIES))
         .thenInvoke((CacheEntry entry, ResultDescriptor result) {
       if (entry.target == part1) {
-        entry.setValue(result, <Source>[library1, library2], []);
+        entry.setValue(result as ResultDescriptor<List<Source>>,
+            <Source>[library1, library2], []);
         return true;
       }
       if (entry.target == part2) {
-        entry.setValue(result, <Source>[library2], []);
+        entry.setValue(
+            result as ResultDescriptor<List<Source>>, <Source>[library2], []);
         return true;
       }
       return false;