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

pkg/analyzer/lib/dart/element/element.dart

Index: pkg/analyzer/lib/dart/element/element.dart
diff --git a/pkg/analyzer/lib/dart/element/element.dart b/pkg/analyzer/lib/dart/element/element.dart
index 57fcdeaf418f7cb57c4a3d4c3c3051dc20525fc1..b829beed070b230382d275e103e98208b085ea62 100644
--- a/pkg/analyzer/lib/dart/element/element.dart
+++ b/pkg/analyzer/lib/dart/element/element.dart
@@ -1156,11 +1156,6 @@ abstract class ExportElement implements Element, UriReferencedElement {
    * directive.
    */
   LibraryElement get exportedLibrary;
-
-  /**
-   * Return `true` if the file referenced by the import's URI exists.
-   */
-  bool get uriExists;
 }
 
 /**
@@ -1346,11 +1341,6 @@ abstract class ImportElement implements Element, UriReferencedElement {
    * prefix, or otherwise does not have an offset.
    */
   int get prefixOffset;
-
-  /**
-   * Return `true` if the file referenced by the import's URI exists.
-   */
-  bool get uriExists;
 }
 
 /**