Serialize data for LibraryElement.getImportsFor

pkg/compiler/lib/src/deferred_load.dart

Index: pkg/compiler/lib/src/deferred_load.dart
diff --git a/pkg/compiler/lib/src/deferred_load.dart b/pkg/compiler/lib/src/deferred_load.dart
index 0f4f8d74eefbb56c0e34a9ee46dfdd154b1785de..b45d301226f580f996426d25a8b5fe5148c3078f 100644
--- a/pkg/compiler/lib/src/deferred_load.dart
+++ b/pkg/compiler/lib/src/deferred_load.dart
@@ -978,6 +978,10 @@ class _DeferredImport {
 
   /// Computes a suggestive name for this import.
   String computeImportDeferName(Compiler compiler) => 'main';
+
+  ImportElement get declaration => null;
+
+  String toString() => 'main';
 }
 
 /// A node in the deferred import graph defined by a deferred import directive.
@@ -1024,4 +1028,6 @@ class _DeclaredDeferredImport implements _DeferredImport {
   }
 
   int get hashCode => declaration.hashCode * 17;
+
+  String toString() => '$declaration';
 }