Work around issue 7218 in Pub.

utils/pub/curl_client.dart

Index: utils/pub/curl_client.dart
diff --git a/utils/pub/curl_client.dart b/utils/pub/curl_client.dart
index e1afc2dbb6c7fc4f77507194669765d4ad97b308..beb60b6b8773ba7837d7b203f87e96019aed708c 100644
--- a/utils/pub/curl_client.dart
+++ b/utils/pub/curl_client.dart
@@ -35,7 +35,7 @@ class CurlClient extends http.BaseClient {
       var headerFile = new Path(tempDir).append("curl-headers").toNativePath();
       var arguments = _argumentsForRequest(request, headerFile);
       var process;
-      return Process.start(executable, arguments).chain((process_) {
+      return startProcess(executable, arguments).chain((process_) {
         process = process_;
         if (requestStream.closed) {
           process.stdin.close();