Add the '--build-summary-only-ast' flag for generating summaries using only ASTs.

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.
 
 library analyzer.src.generated.sdk_io;
 
 import 'dart:collection';
 import 'dart:io';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 264 matching lines @@
     _analysisOptions = options;
   }
 
   @override
   AnalysisContext get context {
     if (_analysisContext == null) {
       _analysisContext = new SdkAnalysisContext(_analysisOptions);
       SourceFactory factory = new SourceFactory([new DartUriResolver(this)]);
       _analysisContext.sourceFactory = factory;
       if (_useSummary) {
-        PackageBundle sdkBundle = _getSummarySdkBundle();
+        PackageBundle sdkBundle = getSummarySdkBundle();
         if (sdkBundle != null) {
           _analysisContext.resultProvider =
               new SdkSummaryResultProvider(_analysisContext, sdkBundle);
         }
       }
     }
     return _analysisContext;
   }
 
   /**
@@ skipping 267 matching lines @@
     Source source = _uriToSourceMap[dartUri];
     if (source == null) {
       source = _mapDartUri(dartUri);
       _uriToSourceMap[dartUri] = source;
     }
     return source;
   }
 
   /**
    * Return the [PackageBundle] for this SDK, if it exists, or `null` otherwise.
+   * This method should not be used outside of `analyzer` and `analyzer_cli`
+   * packages.
    */
-  PackageBundle _getSummarySdkBundle() {
+  PackageBundle getSummarySdkBundle() {
     String rootPath = directory.getAbsolutePath();
     bool strongMode = _analysisOptions?.strongMode ?? false;
     String name = strongMode ? 'strong.sum' : 'spec.sum';
     String path = pathos.join(rootPath, 'lib', '_internal', name);
     try {
       File file = new File(path);
       if (file.existsSync()) {
         List<int> bytes = file.readAsBytesSync();
         return new PackageBundle.fromBuffer(bytes);
       }
@@ skipping 96 matching lines @@
     SdkLibrariesReader_LibraryBuilder libraryBuilder =
         new SdkLibrariesReader_LibraryBuilder(_useDart2jsPaths);
     // If any syntactic errors were found then don't try to visit the AST
     // structure.
     if (!errorListener.errorReported) {
       unit.accept(libraryBuilder);
     }
     return libraryBuilder.librariesMap;
   }
 }