Always add the target library to the store.

pkg/analyzer/lib/src/dart/analysis/analysis_impl.dart

 // Copyright (c) 2017, 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 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/context/context.dart';
@@ skipping 270 matching lines @@
 
     Parser parser = new Parser(file.source, errorListener);
     parser.parseGenericMethodComments = analysisOptions.strongMode;
     CompilationUnit unit = parser.parseCompilationUnit(token);
     unit.lineInfo = lineInfo;
     return unit;
   }
 
   void _resolveFile(AnalysisContext analysisContext, FileState library,
       FileState file, CompilationUnit unit) {
-    if (!file.exists) {
-      Source source = file.source;
-      var unitElement = new CompilationUnitElementImpl(source.shortName);
-      var libraryElement = new LibraryElementImpl(analysisContext, null, -1, 0);
-      unitElement.source = source;
-      unitElement.librarySource = source;
-      libraryElement.definingCompilationUnit = unitElement;
-      unit.element = unitElement;
-      return;
-    }
-
     RecordingErrorListener errorListener = _getErrorListener(file);
 
     String libraryUri = library.uri.toString();
     String unitUri = file.uri.toString();
     CompilationUnitElement unitElement = resynthesizer.getElement(
         new ElementLocationImpl.con3(<String>[libraryUri, unitUri]));
     LibraryElement libraryElement = unitElement.library;
 
     // TODO(scheglov) Hack: set types for top-level variables
     // Otherwise TypeResolverVisitor will set declared types, and because we
@@ skipping 251 matching lines @@
   @override
   String setContents(Source source, String contents) {
     throw new UnimplementedError();
   }
 
   FileState _getFileForSource(Source source) {
     String path = source.fullName;
     return fsState.getFileForPath(path);
   }
 }