Issue 27689. Fix incremental resolution with body modifiers changes.

pkg/analyzer/lib/src/generated/incremental_resolver.dart

Index: pkg/analyzer/lib/src/generated/incremental_resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/incremental_resolver.dart b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
index d847a7bf4c8a292f1e84b77eec4378fe0c67eab4..b7186613a97bee34a5acc7f52cd4a00c19b2bf14 100644
--- a/pkg/analyzer/lib/src/generated/incremental_resolver.dart
+++ b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
@@ -665,6 +665,14 @@ class PoorMansIncrementalResolver {
             } else if (oldParent is FunctionBody && newParent is FunctionBody) {
               if (oldParent is BlockFunctionBody &&
                   newParent is BlockFunctionBody) {
+                if (oldParent.isAsynchronous != newParent.isAsynchronous) {
+                  logger.log('Failure: body async mismatch.');
+                  return false;
+                }
+                if (oldParent.isGenerator != newParent.isGenerator) {
+                  logger.log('Failure: body generator mismatch.');
+                  return false;
+                }
                 oldNode = oldParent;
                 newNode = newParent;
                 found = true;