Issue 8742. Preserve leading line comments during java2dart translation.

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

Index: pkg/analyzer/lib/src/generated/sdk_io.dart
diff --git a/pkg/analyzer/lib/src/generated/sdk_io.dart b/pkg/analyzer/lib/src/generated/sdk_io.dart
index f3d905c2de31a562c6e31eec437e66ab9eef9db6..eaca50f878c64e807f99ac6eed1c9009e0760f60 100644
--- a/pkg/analyzer/lib/src/generated/sdk_io.dart
+++ b/pkg/analyzer/lib/src/generated/sdk_io.dart
@@ -473,6 +473,7 @@ class SdkLibrariesReader {
     Parser parser = new Parser(source, errorListener);
     CompilationUnit unit = parser.parseCompilationUnit(scanner.tokenize());
     SdkLibrariesReader_LibraryBuilder libraryBuilder = new SdkLibrariesReader_LibraryBuilder();
+    // If any syntactic errors were found then don't try to visit the AST structure.
     if (!errorListener.errorReported) {
       unit.accept(libraryBuilder);
     }