Make conflicting summary check configurable

pkg/analyzer/lib/src/summary/package_bundle_reader.dart

 import 'dart:io' as io;
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/resolver.dart' show TypeProvider;
@@ skipping 380 matching lines @@
    * Map from the URI of a library to the summary path that contained it.
    */
   final Map<String, String> uriToSummaryPath = <String, String>{};
 
   /**
    * List of summary paths.
    */
   final Iterable<String> _summaryPaths;
 
   /**
+   * If true, do not accept multiple summaries that contain the same Dart uri.
+   */
+  bool _disallowOverlappingSummaries;
+
+  /**
    * Create a [SummaryDataStore] and populate it with the summaries in
    * [summaryPaths].  If [recordDependencyInfo] is `true`, record
    * [PackageDependencyInfo] for each summary, for later access via
    * [dependencies].
    */
   SummaryDataStore(Iterable<String> summaryPaths,
-      {bool recordDependencyInfo: false, ResourceProvider resourceProvider})
+      {bool recordDependencyInfo: false,
+      bool disallowOverlappingSummaries: false,
+      ResourceProvider resourceProvider})
       : _summaryPaths = summaryPaths,
+        _disallowOverlappingSummaries = disallowOverlappingSummaries,
         dependencies =
             recordDependencyInfo ? <PackageDependencyInfoBuilder>[] : null {
     summaryPaths.forEach((String path) => _fillMaps(path, resourceProvider));
   }
 
   /**
    * Add the given [bundle] loaded from the file with the given [path].
    */
   void addBundle(String path, PackageBundle bundle) {
     bundles.add(bundle);
@@ skipping 15 matching lines @@
       }
       dependencies.add(new PackageDependencyInfoBuilder(
           includedPackageNames: includedPackageNames.toList()..sort(),
           includesDartUris: includesDartUris,
           includesFileUris: includesFileUris,
           apiSignature: bundle.apiSignature,
           summaryPath: path));
     }
     for (int i = 0; i < bundle.unlinkedUnitUris.length; i++) {
       String uri = bundle.unlinkedUnitUris[i];
-      if (uriToSummaryPath.containsKey(uri) &&
+      if (_disallowOverlappingSummaries &&
+          uriToSummaryPath.containsKey(uri) &&
           (uriToSummaryPath[uri] != path)) {
         throw new ConflictingSummaryException(
             _summaryPaths, uri, uriToSummaryPath[uri], path);
       }
       uriToSummaryPath[uri] = path;
       addUnlinkedUnit(uri, bundle.unlinkedUnits[i]);
     }
     for (int i = 0; i < bundle.linkedLibraryUris.length; i++) {
       String uri = bundle.linkedLibraryUris[i];
       addLinkedLibrary(uri, bundle.linkedLibraries[i]);
@@ skipping 45 matching lines @@
       var file = resourceProvider.getFile(path);
       buffer = file.readAsBytesSync();
     } else {
       io.File file = new io.File(path);
       buffer = file.readAsBytesSync();
     }
     PackageBundle bundle = new PackageBundle.fromBuffer(buffer);
     addBundle(path, bundle);
   }
 }