Get binstubs working on Windows.

sdk/lib/_internal/pub/bin/async_compile.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.
 
 import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:analyzer/src/services/formatter_impl.dart';
 import 'package:async_await/async_await.dart' as async_await;
 import 'package:path/path.dart' as p;
@@ skipping 53 matching lines @@
     stderr.writeln(ex);
     stderr.writeln();
     stderr.writeln(
         "Usage: dart async_compile.dart [--verbose] [--force] <build dir>");
     exit(64);
   }
 
   // See what version (i.e. Git commit) of the async-await compiler we
   // currently have. If this is different from the version that was used to
   // compile the sources, recompile everything.
-  var result = Process.runSync("git", ["rev-parse", "HEAD"], workingDirectory:
-      p.join(sourceDir, "../../../../third_party/pkg/async_await"));
-  if (result.exitCode != 0) {
-    stderr.writeln("Could not get Git revision of async_await compiler.");
-    exit(1);
-  }
-
-  var currentCommit = result.stdout.trim();
+  var currentCommit = _getCurrentCommit();
 
   var readmePath = p.join(generatedDir, "README.md");
   var lastCommit;
   var readme = new File(readmePath).readAsStringSync();
   var match = _commitPattern.firstMatch(readme);
   if (match == null) {
     stderr.writeln("Could not find compiler commit hash in README.md.");
     exit(1);
   }
 
@@ skipping 43 matching lines @@
     if (verbose) print("Updated README.md");
   }
 
   if (numCompiled > 0) _generateSnapshot(buildDir);
 
   if (verbose) print("Compiled $numCompiled out of $numFiles files");
 
   if (hadFailure) exit(1);
 }
 
+String _getCurrentCommit() {
+  var command = "git";
+  var args = ["rev-parse", "HEAD"];
+
+  // Spawning a process on Windows will not look for the executable in the
+  // system path so spawn git through a shell to find it.
+  if (Platform.operatingSystem == "windows") {
+    command = "cmd";
+    args = ["/c", "git"]..addAll(args);
+  }
+
+  var result = Process.runSync(command, args, workingDirectory:
+      p.join(sourceDir, "../../../../third_party/pkg/async_await"));
+  if (result.exitCode != 0) {
+    stderr.writeln("Could not get Git revision of async_await compiler.");
+    exit(1);
+  }
+
+  return result.stdout.trim();
+}
+
 void _compile(String sourcePath, String source, String destPath) {
   var destDir = new Directory(p.dirname(destPath));
   destDir.createSync(recursive: true);
 
   source = _translateAsyncAwait(sourcePath, source);
   if (source != null) source = _fixDart2jsImports(sourcePath, source, destPath);
 
   if (source == null) {
     // If the async compile fails, delete the file so that we don't try to
     // run the stale previous output and so that we try to recompile it later.
@@ skipping 82 matching lines @@
 ///
 /// This swallows errors to accommodate multiple compilers running concurrently.
 /// Since they will produce the same output anyway, a failure of one is fine.
 void _writeFile(String path, String contents) {
   try {
     new File(path).writeAsStringSync(contents);
   } on IOException catch (ex) {
     // Do nothing.
   }
 }