Fix handling of sdk path when building SDK summaries.

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

Index: pkg/analyzer/lib/src/summary/summary_file_builder.dart
diff --git a/pkg/analyzer/lib/src/summary/summary_file_builder.dart b/pkg/analyzer/lib/src/summary/summary_file_builder.dart
index 682973c8ce2cd4f65cbc78d4a7047b99404f231a..c9c835e105c1def5e11d4056307a4829423359e4 100644
--- a/pkg/analyzer/lib/src/summary/summary_file_builder.dart
+++ b/pkg/analyzer/lib/src/summary/summary_file_builder.dart
@@ -116,8 +116,8 @@ class SummaryBuilder {
     // 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;