Issue 25733. Built-in itentifiers are not permitted as prefixes.

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

Index: pkg/analyzer/lib/src/generated/error_verifier.dart
diff --git a/pkg/analyzer/lib/src/generated/error_verifier.dart b/pkg/analyzer/lib/src/generated/error_verifier.dart
index c9bcf4350f783862dabd312a0e328b48b4b93350..1fa5eae09db4805cfbc74551a068dbc160ea4184 100644
--- a/pkg/analyzer/lib/src/generated/error_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/error_verifier.dart
@@ -900,6 +900,10 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
   @override
   Object visitImportDirective(ImportDirective node) {
     ImportElement importElement = node.element;
+    if (node.prefix != null) {
+      _checkForBuiltInIdentifierAsName(
+          node.prefix, CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_PREFIX_NAME);
+    }
     if (importElement != null) {
       _checkForImportDuplicateLibraryName(node, importElement);
       _checkForImportInternalLibrary(node, importElement);