Change Process.start to return a future that completes with a

utils/pub/io.dart

Index: utils/pub/io.dart
diff --git a/utils/pub/io.dart b/utils/pub/io.dart
index bef2b2ae37e5f7d648c3203e3ad66e9c6cafec23..4a338177d5e2536fec7b609093c7a3dbfedd2ff7 100644
--- a/utils/pub/io.dart
+++ b/utils/pub/io.dart
@@ -495,48 +495,51 @@ Future<PubProcessResult> runProcess(String executable, List<String> args,
   }
   options.environment = environment;
 
-  final process = Process.start(executable, args, options);
-
-  final outStream = new StringInputStream(process.stdout);
-  final processStdout = <String>[];
-
-  final errStream = new StringInputStream(process.stderr);
-  final processStderr = <String>[];
-
   final completer = new Completer<PubProcessResult>();
 
-  checkComplete() {
-    // Wait until the process is done and its output streams are closed.
-    if (!pipeStdout && !outStream.closed) return;
-    if (!pipeStderr && !errStream.closed) return;
-    if (exitCode == null) return;
+  var processFuture = Process.start(executable, args, options);
+  processFuture.then((process) {
+    final outStream = new StringInputStream(process.stdout);
+    final processStdout = <String>[];
 
-    completer.complete(new PubProcessResult(
-        processStdout, processStderr, exitCode));
-  }
+    final errStream = new StringInputStream(process.stderr);
+    final processStderr = <String>[];
 
-  if (pipeStdout) {
-    process.stdout.pipe(stdout, close: false);
-  } else {
-    outStream.onLine   = () => processStdout.add(outStream.readLine());
-    outStream.onClosed = checkComplete;
-    outStream.onError  = (error) => completer.completeException(error);
-  }
+    checkComplete() {
+      // Wait until the process is done and its output streams are closed.
+      if (!pipeStdout && !outStream.closed) return;
+      if (!pipeStderr && !errStream.closed) return;
+      if (exitCode == null) return;
 
-  if (pipeStderr) {
-    process.stderr.pipe(stderr, close: false);
-  } else {
-    errStream.onLine   = () => processStderr.add(errStream.readLine());
-    errStream.onClosed = checkComplete;
-    errStream.onError  = (error) => completer.completeException(error);
-  }
+      completer.complete(new PubProcessResult(
+          processStdout, processStderr, exitCode));
+    }
 
-  process.onExit = (actualExitCode) {
-    exitCode = actualExitCode;
-    checkComplete();
-  };
+    if (pipeStdout) {
+      process.stdout.pipe(stdout, close: false);
+    } else {
+      outStream.onLine   = () => processStdout.add(outStream.readLine());
+      outStream.onClosed = checkComplete;
+      outStream.onError  = (error) => completer.completeException(error);
+    }
 
-  process.onError = (error) => completer.completeException(error);
+    if (pipeStderr) {
+      process.stderr.pipe(stderr, close: false);
+    } else {
+      errStream.onLine   = () => processStderr.add(errStream.readLine());
+      errStream.onClosed = checkComplete;
+      errStream.onError  = (error) => completer.completeException(error);
+    }
+
+    process.onExit = (actualExitCode) {
+      exitCode = actualExitCode;
+      checkComplete();
+    };
+  });
+  processFuture.handleException((error) {
+    completer.completeException(error);
+    return true;
+  });
 
   return completer.future;
 }
@@ -640,20 +643,19 @@ Future<bool> extractTarGz(InputStream stream, destination) {
     return _extractTarGzWindows(stream, destination);
   }
 
-  var process = Process.start("tar",
-      ["--extract", "--gunzip", "--directory", destination]);
   var completer = new Completer<int>();
-
-  process.onExit = completer.complete;
-  process.onError = completer.completeException;
-
-  // Wait for the process to be fully started before writing to its
-  // stdin stream.
-  process.onStart = () {
+  var processFuture = Process.start("tar",
+      ["--extract", "--gunzip", "--directory", destination]);
+  processFuture.then((process) {
+    process.onExit = completer.complete;
     stream.pipe(process.stdin);
     process.stdout.pipe(stdout, close: false);
     process.stderr.pipe(stderr, close: false);
-  };
+  });
+  processFuture.handleException((error) {
+    completer.completeException(error);
+    return true;
+  });
 
   return completer.future.transform((exitCode) => exitCode == 0);
 }