Fix file name handling on windows

pkg/dev_compiler/lib/src/compiler/compiler.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:collection' show HashSet, Queue;
 import 'dart:convert' show BASE64, JSON, UTF8;
 import 'dart:io' show File;
 import 'package:analyzer/dart/element/element.dart' show LibraryElement;
 import 'package:analyzer/analyzer.dart'
     show AnalysisError, CompilationUnit, ErrorSeverity;
@@ skipping 93 matching lines @@
   /// summaries before calling this method.
   JSModuleFile compile(BuildUnit unit, CompilerOptions options) {
     var trees = <CompilationUnit>[];
     var errors = <AnalysisError>[];
 
     var librariesToCompile = new Queue<LibraryElement>();
 
     var compilingSdk = false;
     for (var sourcePath in unit.sources) {
       var sourceUri = Uri.parse(sourcePath);
-      if (sourceUri.scheme == '') {
+      if (sourceUri.scheme == 'dart') {
+        compilingSdk = true;
+      } else if (sourceUri.scheme != 'package') {
         sourceUri = path.toUri(path.absolute(sourcePath));
-      } else if (sourceUri.scheme == 'dart') {
-        compilingSdk = true;
       }
       Source source = context.sourceFactory.forUri2(sourceUri);
 
       var fileUsage = 'You need to pass at least one existing .dart file as an'
           ' argument.';
       if (source == null) {
         throw new UsageException(
             'Could not create a source for "$sourcePath". The file name is in'
             ' the wrong format or was not found.',
             fileUsage);
@@ skipping 368 matching lines @@
     Map sourceMap, String sourceMapPath, Map<String, String> bazelMappings) {
   var dir = path.dirname(sourceMapPath);
   var map = new Map.from(sourceMap);
   var list = new List.from(map['sources']);
   map['sources'] = list;
   String transformUri(String uri) {
     var match = bazelMappings[path.absolute(uri)];
     if (match != null) return match;
 
     // Fall back to a relative path.
-    return path.toUri(path.relative(path.fromUri(uri), from: dir)).toString();
+    return path.toUri(path.relative(uri, from: dir)).toString();
   }
 
   for (int i = 0; i < list.length; i++) {
     list[i] = transformUri(list[i]);
   }
   map['file'] = transformUri(map['file']);
   return map;
 }