Fix resolveRelativeUri() to handle correctly empty contained Uri(s).

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/src/dart/scanner/reader.dart';
@@ skipping 301 matching lines @@
    */
   Source addNamedSource(String filePath, String contents) {
     CompilationUnit unit = _parseText(contents);
     UnlinkedUnitBuilder unlinkedUnit = serializeAstUnlinked(unit);
     _filesToLink.uriToUnit[absUri(filePath)] = unlinkedUnit;
     // Tests using SummaryLinkerTest don't actually need the returned
     // Source, so we can safely return `null`.
     return null;
   }
 
-  LinkerInputs createLinkerInputs(String text, {String path: '/test.dart'}) {
-    Uri testDartUri = Uri.parse(absUri(path));
+  LinkerInputs createLinkerInputs(String text, {String path: '/test.dart', String uri}) {
+    uri ??= absUri(path);
+    Uri testDartUri = Uri.parse(uri);
     CompilationUnit unit = _parseText(text);
     UnlinkedUnitBuilder unlinkedDefiningUnit = serializeAstUnlinked(unit);
     _filesToLink.uriToUnit[testDartUri.toString()] = unlinkedDefiningUnit;
     LinkerInputs linkerInputs = new LinkerInputs(
         allowMissingFiles,
         _filesToLink.uriToUnit,
         testDartUri,
         unlinkedDefiningUnit,
         _filesToLink.summaryDataStore.linkedMap,
         _filesToLink.summaryDataStore.unlinkedMap);
     // Reset _filesToLink in case the test needs to start a new package bundle.
     _filesToLink = new _FilesToLink();
     return linkerInputs;
   }
 
   /**
    * Link together the given file, along with any other files passed to
    * [addNamedSource], to form a package bundle.  Reset the state of the buffers
    * accumulated by [addNamedSource] and [addBundle] so that further bundles
    * can be created.
    */
   PackageBundleBuilder createPackageBundle(String text,
-      {String path: '/test.dart'}) {
+      {String path: '/test.dart', String uri}) {
     PackageBundleAssembler assembler = new PackageBundleAssembler();
     assembler.recordDependencies(_filesToLink.summaryDataStore);
-    LinkerInputs linkerInputs = createLinkerInputs(text, path: path);
+    LinkerInputs linkerInputs = createLinkerInputs(text, path: path, uri: uri);
     Map<String, LinkedLibraryBuilder> linkedLibraries = link(
         linkerInputs.linkedLibraries,
         linkerInputs.getDependency,
         linkerInputs.getUnit,
         true);
     linkedLibraries.forEach(assembler.addLinkedLibrary);
     linkerInputs._uriToUnit.forEach((String uri, UnlinkedUnit unit) {
       // Note: it doesn't matter what we store for the hash because it isn't
       // used in these tests.
       assembler.addUnlinkedUnitWithHash(uri, unit, 'HASH');
@@ skipping 25 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);
 }