Use absolute URIs for LinkedDependency.uri/parts.

pkg/analyzer/test/src/summary/summarize_ast_test.dart

 // Copyright (c) 2016, 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.
 
 library analyzer.test.src.summary.summarize_ast_test;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/listener.dart';
@@ skipping 206 matching lines @@
     if (linkedLibrary == null && !_allowMissingFiles) {
       Set<String> librariesAvailable = sdkLibraries.keys.toSet();
       librariesAvailable.addAll(_dependentLinkedLibraries.keys);
       fail('Linker unexpectedly requested LinkedLibrary for "$absoluteUri".'
           '  Libraries available: ${librariesAvailable.toList()}');
     }
     return linkedLibrary;
   }
 
   UnlinkedUnit getUnit(String absoluteUri) {
+    if (absoluteUri == null) {
+      return null;
+    }
     UnlinkedUnit unit = _uriToUnit[absoluteUri] ??
         SerializedMockSdk.instance.uriToUnlinkedUnit[absoluteUri] ??
         _dependentUnlinkedUnits[absoluteUri];
     if (unit == null && !_allowMissingFiles) {
       fail('Linker unexpectedly requested unit for "$absoluteUri".');
     }
     return unit;
   }
 }
 
@@ skipping 106 matching lines @@
    * passed to [addNamedSource].
    */
   Map<String, UnlinkedUnitBuilder> uriToUnit = <String, UnlinkedUnitBuilder>{};
 
   /**
    * Information about summaries to be included in the link process.
    */
   SummaryDataStore summaryDataStore =
       new SummaryDataStore([], recordDependencyInfo: true);
 }