Fix PackageUriResolver.restoreAbsolute on Windows

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.
 
 library engine.source.io;
 
 import 'dart:collection';
 
 import 'engine.dart';
 import 'java_core.dart';
@@ skipping 449 matching lines @@
             canonicalFile, actualUri != null ? actualUri : uri);
       }
     }
     return new FileBasedSource(
         getCanonicalFile(_packagesDirectories[0], pkgName, relPath),
         actualUri != null ? actualUri : uri);
   }
 
   @override
   Uri restoreAbsolute(Source source) {
-    String sourcePath = source.fullName;
+    String sourceUri = _toFileUri(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);
+            String pkgCanonicalUri = _toFileUri(pkgFolder.getCanonicalPath());
+            if (sourceUri.startsWith(pkgCanonicalUri)) {
+              String relPath = sourceUri.substring(pkgCanonicalUri.length);
               return parseUriWithException(
                   "$PACKAGE_SCHEME:${pkgFolder.getName()}$relPath");
             }
           } catch (e) {}
         }
       }
     }
     return null;
   }
 
   /**
    * @return `true` if "file" was found in "packagesDir", and it is part of the "lib" folder
    *         of the application that contains in this "packagesDir".
    */
   bool _isSelfReference(JavaFile packagesDir, JavaFile file) {
     JavaFile rootDir = packagesDir.getParentFile();
     if (rootDir == null) {
       return false;
     }
     String rootPath = rootDir.getAbsolutePath();
     String filePath = file.getAbsolutePath();
     return filePath.startsWith("$rootPath/lib");
   }
 
   /**
+   * Convert the given file path to a "file:" URI.  On Windows, this transforms
+   * backslashes to forward slashes.
+   */
+  String _toFileUri(String filePath) =>
+      JavaFile.pathContext.toUri(filePath).toString();
+
+  /**
    * Return `true` if the given URI is a `package` URI.
    *
    * @param uri the URI being tested
    * @return `true` if the given URI is a `package` URI
    */
   static bool isPackageUri(Uri uri) => PACKAGE_SCHEME == uri.scheme;
 }
 
 /**
  * Instances of the class `RelativeFileUriResolver` resolve `file` URI's.
@@ skipping 38 matching lines @@
   }
 
   /**
    * Return `true` if the given URI is a `file` URI.
    *
    * @param uri the URI being tested
    * @return `true` if the given URI is a `file` URI
    */
   static bool isFileUri(Uri uri) => uri.scheme == FILE_SCHEME;
 }