Workaround for accessing part sources while resolving a library.

pkg/analyzer/lib/src/dart/analysis/driver.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.
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:typed_data';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart' show CompilationUnitElement;
@@ skipping 635 matching lines @@
       // Prepare the library file - the file itself, or the known library.
       FileState libraryFile = getLibraryFile(file);
       if (libraryFile == null) {
         return null;
       }
 
       _LibraryContext libraryContext = _createLibraryContext(libraryFile);
       AnalysisContext analysisContext = _createAnalysisContext(libraryContext);
       try {
         analysisContext.setContents(file.source, file.content);
+
+        // TODO(scheglov) Remove this.
+        // https://github.com/dart-lang/sdk/issues/28110
+        analysisContext.setContents(libraryFile.source, libraryFile.content);
+        for (FileState part in libraryFile.partedFiles) {
+          if (part.exists) {
+            analysisContext.setContents(part.source, part.content);
+          }
+        }
+
         CompilationUnit resolvedUnit = analysisContext.resolveCompilationUnit2(
             file.source, libraryFile.source);
         List<AnalysisError> errors = analysisContext.computeErrors(file.source);
         AnalysisDriverUnitIndexBuilder index = indexUnit(resolvedUnit);
 
         // Store the result into the cache.
         List<int> bytes;
         {
           bytes = new AnalysisDriverResolvedUnitBuilder(
                   errors: errors
@@ skipping 918 matching lines @@
           libraryDeclarations.add(new TopLevelDeclarationInSource(
               file.source, declaration, isExported));
         }
       }
     }
 
     // We're not done yet.
     return false;
   }
 }