Fix summary handling of unresolved imports, exports, and parts.

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

Index: pkg/analyzer/lib/src/summary/index_unit.dart
diff --git a/pkg/analyzer/lib/src/summary/index_unit.dart b/pkg/analyzer/lib/src/summary/index_unit.dart
index c1bbae530e9b5549611a956d616053fd21b2a403..5a9cb479fa000cae4ad9a4bb814e3b2c85056eab 100644
--- a/pkg/analyzer/lib/src/summary/index_unit.dart
+++ b/pkg/analyzer/lib/src/summary/index_unit.dart
@@ -23,7 +23,9 @@ class IndexElementInfo {
 
   factory IndexElementInfo(Element element) {
     IndexSyntheticElementKind kind = IndexSyntheticElementKind.notSynthetic;
-    if (element.isSynthetic) {
+    if (element is LibraryElement || element is CompilationUnitElement) {
+      kind = IndexSyntheticElementKind.unit;
+    } else if (element.isSynthetic) {
       if (element is ConstructorElement) {
         kind = IndexSyntheticElementKind.constructor;
         element = element.enclosingElement;
@@ -60,8 +62,6 @@ class IndexElementInfo {
         throw new ArgumentError(
             'Unsupported synthetic element ${element.runtimeType}');
       }
-    } else if (element is LibraryElement || element is CompilationUnitElement) {
-      kind = IndexSyntheticElementKind.unit;
     }
     return new IndexElementInfo._(element, kind);
   }