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

pkg/analyzer/tool/task_dependency_graph/tasks.dot

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // This file has been automatically generated.  Please do not edit it manually.
 // To regenerate the file, use the script
 // "pkg/analyzer/tool/task_dependency_graph/generate.dart".
 //
 // To render this graph using Graphviz (www.graphviz.org) use the command:
 // "dot tasks.dot -Tpdf -O".
@@ skipping 171 matching lines @@
   LIBRARY_UNIT_ERRORS -> dartErrorsForUnit
   LIBRARY_UNIT_ERRORS [shape=box]
   LINE_INFO -> DartErrorsTask
   LINE_INFO -> ParseDartTask
   LINE_INFO [shape=box]
   LINTS -> LibraryUnitErrorsTask
   LINTS [shape=box]
   LibraryErrorsReadyTask -> LIBRARY_ERRORS_READY
   LibraryUnitErrorsTask -> LIBRARY_UNIT_ERRORS
   MODIFICATION_TIME -> BuildDirectiveElementsTask
+  MODIFICATION_TIME -> BuildLibraryElementTask
   MODIFICATION_TIME -> ParseDartTask
   MODIFICATION_TIME -> ScanDartTask
   MODIFICATION_TIME -> VerifyUnitTask
   MODIFICATION_TIME [shape=box]
   PARSED_UNIT -> BuildCompilationUnitElementTask
   PARSED_UNIT [shape=box]
   PARSE_ERRORS -> dartErrorsForSource
   PARSE_ERRORS [shape=box]
   PENDING_ERRORS -> VerifyUnitTask
   PENDING_ERRORS [shape=box]
@@ skipping 163 matching lines @@
   VARIABLE_REFERENCE_ERRORS -> LibraryUnitErrorsTask
   VARIABLE_REFERENCE_ERRORS [shape=box]
   VERIFY_ERRORS -> LibraryUnitErrorsTask
   VERIFY_ERRORS [shape=box]
   VerifyUnitTask -> VERIFY_ERRORS
   dartErrorsForSource -> DartErrorsTask
   dartErrorsForSource [shape=hexagon]
   dartErrorsForUnit -> DartErrorsTask
   dartErrorsForUnit [shape=hexagon]
 }