Fix a couple bugs in r42055.

sdk/lib/_internal/pub_generated/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 43 matching lines @@
     var rest = parser.parse(arguments).rest;
     if (rest.isEmpty) {
       throw new FormatException('Missing build directory.');
     } else if (rest.length > 1) {
       throw new FormatException(
           'Unexpected arguments: ${rest.skip(1).join(" ")}.');
     }
 
     buildDir = rest.first;
   } on FormatException catch (ex) {
-    print(ex);
-    print();
-    print("Usage: dart async_compile.dart [--verbose] [--force] <build dir>");
+    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 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) {
-    print("Could not find compiler commit hash in README.md.");
+    stderr.writeln("Could not find compiler commit hash in README.md.");
     exit(1);
   }
 
   lastCommit = match[0];
 
   var numFiles = 0;
   var numCompiled = 0;
 
   // Compile any modified or missing files.
   var sources = new Set();
@@ skipping 52 matching lines @@
   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) {
-    print("Could not get Git revision of async_await compiler.");
+    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);
 
@@ skipping 21 matching lines @@
 
   try {
     source = async_await.compile(source);
 
     // Reformat the result since the compiler ditches all whitespace.
     // TODO(rnystrom): Remove when this is fixed:
     // https://github.com/dart-lang/async_await/issues/12
     var result = new CodeFormatter().format(CodeKind.COMPILATION_UNIT, source);
     return result.source;
   } catch (ex) {
-    print("Async compile failed on $sourcePath:\n$ex");
+    stderr.writeln("Async compile failed on $sourcePath:\n$ex");
     hadFailure = true;
     return null;
   }
 }
 
 /// Fix relative imports to dart2js libraries.
 ///
 /// Pub imports dart2js using relative imports that reach outside of pub's
 /// source tree. Since the build directory is in a different location, we need
 /// to fix those to be valid relative imports from the build directory.
@@ skipping 12 matching lines @@
 
   var entrypoint = p.join(generatedDir, 'bin/pub.dart');
   var packageRoot = p.join(buildDir, 'packages');
   var snapshot = p.join(buildDir, 'dart-sdk/bin/snapshots/pub.dart.snapshot');
 
   var result = Process.runSync(
       Platform.executable,
       ["--package-root=$packageRoot", "--snapshot=$snapshot", entrypoint]);
 
   if (result.exitCode != 0) {
-    print("Failed to generate snapshot:");
-    if (result.stderr.trim().isNotEmpty) print(result.stderr);
-    if (result.stdout.trim().isNotEmpty) print(result.stdout);
+    stderr.writeln("Failed to generate snapshot:");
+    if (result.stderr.trim().isNotEmpty) stderr.writeln(result.stderr);
+    if (result.stdout.trim().isNotEmpty) stderr.writeln(result.stdout);
     exit(result.exitCode);
   }
 
   if (verbose) print("Created pub snapshot");
 }
 
 /// Deletes the file at [path], ignoring any IO errors that occur.
 ///
 /// This swallows errors to accommodate multiple compilers running concurrently.
 /// Since they will produce the same output anyway, a failure of one is fine.
 void _deleteFile(String path) {
   try {
     new File(path).deleteSync();
   } on IOException catch (ex) {
     // Do nothing.
   }
 }
 
 /// Writes [contents] to [path], ignoring any IO errors that occur.
 ///
 /// 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.
   }
 }