Issue 8742. Preserve leading line comments during java2dart translation.

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.sdk.io;
 
 import 'java_core.dart';
@@ skipping 455 matching lines @@
    * @param source the source of the library file
    * @param libraryFileContents the contents from the library file
    * @return the library map read from the given source
    */
   LibraryMap readFrom2(Source source, String libraryFileContents) {
     BooleanErrorListener errorListener = new BooleanErrorListener();
     Scanner scanner = new Scanner(source, new CharSequenceReader(new CharSequence(libraryFileContents)), errorListener);
     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);
     }
     return libraryBuilder.librariesMap;
   }
 }
 
 class SdkLibrariesReader_LibraryBuilder extends RecursiveASTVisitor<Object> {
   /**
    * The prefix added to the name of a library to form the URI used in code to reference the
@@ skipping 67 matching lines @@
               }
             }
           }
         }
       }
       librariesMap.setLibrary(libraryName, library);
     }
     return null;
   }
 }