Fix handling of sdk path when building SDK summaries.

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

 // Copyright (c) 2016, 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.summary.summary_file_builder;
 
 import 'dart:collection';
 import 'dart:io' as io;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 98 matching lines @@
    * Create an SDK summary builder for the dart SDK at the given [sdkPath],
    * using this [config].
    */
   factory SummaryBuilder.forSdk(String sdkPath, SummaryBuildConfig config) {
     bool strongMode = config.strongMode;
 
     //
     // Prepare SDK.
     //
     ResourceProvider resourceProvider = PhysicalResourceProvider.INSTANCE;
-    FolderBasedDartSdk sdk = new FolderBasedDartSdk(resourceProvider,
-        FolderBasedDartSdk.defaultSdkDirectory(resourceProvider), strongMode);
+    FolderBasedDartSdk sdk = new FolderBasedDartSdk(
+        resourceProvider, resourceProvider.getFolder(sdkPath), strongMode);
     sdk.useSummary = false;
     sdk.analysisOptions = new AnalysisOptionsImpl()..strongMode = strongMode;
 
     //
     // Prepare 'dart:' URIs to serialize.
     //
     Set<String> uriSet =
         sdk.sdkLibraries.map((SdkLibrary library) => library.shortName).toSet();
     if (!strongMode) {
       uriSet.add('dart:html/nativewrappers.dart');
@@ skipping 83 matching lines @@
     element.exportedLibraries.forEach((e) => _serializeLibrary(e.source));
     // Index every unit of the library.
     for (CompilationUnitElement unitElement in element.units) {
       Source unitSource = unitElement.source;
       CompilationUnit unit =
           context.resolveCompilationUnit2(unitSource, source);
       indexAssembler.indexUnit(unit);
     }
   }
 }