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..6bc479ba1c95b9a2aaca58dca6ab3c0a2805cf25 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -1420,8 +1420,8 @@ class BuildLibraryElementTask extends SourceBasedAnalysisTask {
     //
     // Create and populate the library element.
     //
-    LibraryElementImpl libraryElement =
-        new LibraryElementImpl.forNode(context, libraryNameNode);
+    LibraryElementImpl libraryElement = new LibraryElementImpl.forNode(
+        context.getContextFor(librarySource), libraryNameNode);
     libraryElement.definingCompilationUnit = definingCompilationUnitElement;
     libraryElement.entryPoint = entryPoint;
     libraryElement.parts = sourcedCompilationUnits;