Create LibraryElement with SDK context for SDK sources.

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index 810e1097cdf7bb06ac5d71de235a3fa4434357a3..e8443f87e0a9e61b75b5d019f4b110562fc7ffd2 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -1420,8 +1420,13 @@ class BuildLibraryElementTask extends SourceBasedAnalysisTask {
     //
     // Create and populate the library element.
     //
+    AnalysisContext owningContext = context;
+    if (context is InternalAnalysisContext) {
+      InternalAnalysisContext internalContext = context;
+      owningContext = internalContext.getContextFor(librarySource);
+    }
     LibraryElementImpl libraryElement =
-        new LibraryElementImpl.forNode(context, libraryNameNode);
+        new LibraryElementImpl.forNode(owningContext, libraryNameNode);
     libraryElement.definingCompilationUnit = definingCompilationUnitElement;
     libraryElement.entryPoint = entryPoint;
     libraryElement.parts = sourcedCompilationUnits;