Issue 21451. Fix for 'Add import' Quick Fix in case when package roots is in use.

pkg/analyzer/lib/src/generated/source_io.dart

 // Copyright (c) 2014, 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 code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.source.io;
 
 import 'source.dart';
@@ skipping 381 matching lines @@
           uri = canonicalFile.toURI();
         }
         return new FileBasedSource.con2(uri, canonicalFile);
       }
     }
     return new FileBasedSource.con2(uri, getCanonicalFile(_packagesDirectories[0], pkgName, relPath));
   }
 
   @override
   Uri restoreAbsolute(Source source) {
-    if (source is FileBasedSource) {
-      String sourcePath = source.file.getPath();
-      for (JavaFile packagesDirectory in _packagesDirectories) {
-        List<JavaFile> pkgFolders = packagesDirectory.listFiles();
-        if (pkgFolders != null) {
-          for (JavaFile pkgFolder in pkgFolders) {
-            try {
-              String pkgCanonicalPath = pkgFolder.getCanonicalPath();
-              if (sourcePath.startsWith(pkgCanonicalPath)) {
-                String relPath = sourcePath.substring(pkgCanonicalPath.length);
-                return parseUriWithException("$PACKAGE_SCHEME:${pkgFolder.getName()}$relPath");
-              }
-            } catch (e) {
+    String sourcePath = source.fullName;
+    for (JavaFile packagesDirectory in _packagesDirectories) {
+      List<JavaFile> pkgFolders = packagesDirectory.listFiles();
+      if (pkgFolders != null) {
+        for (JavaFile pkgFolder in pkgFolders) {
+          try {
+            String pkgCanonicalPath = pkgFolder.getCanonicalPath();
+            if (sourcePath.startsWith(pkgCanonicalPath)) {
+              String relPath = sourcePath.substring(pkgCanonicalPath.length);
+              return parseUriWithException("$PACKAGE_SCHEME:${pkgFolder.getName()}$relPath");
             }
+          } catch (e) {
           }
         }
       }
     }
     return null;
   }
 
   /**
    * Answer the canonical file for the specified package.
    *
@@ skipping 75 matching lines @@
       for (JavaFile dir in _relativeDirectories) {
         JavaFile file = new JavaFile.relative(dir, filePath);
         if (file.exists()) {
           return new FileBasedSource.con2(uri, file);
         }
       }
     }
     return null;
   }
 }