Changed headless browser profile dir to use Default profile path

Bug: 775703
Change-Id: Id56b1abd8355667d93a4d5b612af6e7a08a3577e
Reviewed-on: https://chromium-review.googlesource.com/743144Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: David Vallet <dvallet@chromium.org>
Commit-Queue: David Vallet <dvallet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512647}

headless/lib/browser/headless_browser_context_impl.cc

@@ -201,7 +201,8 @@ void HeadlessBrowserContextImpl::Close() {
 
 void HeadlessBrowserContextImpl::InitWhileIOAllowed() {
   if (!context_options_->user_data_dir().empty()) {
-    path_ = context_options_->user_data_dir();
+    path_ =
+        context_options_->user_data_dir().Append(FILE_PATH_LITERAL("Default"));
   } else {
     PathService::Get(base::DIR_EXE, &path_);
   }