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### Issue Details

* **Electron Version:**
  * 7.0.0
* **Operating System:**
  * Ubuntu 18.04 (KDE Neon)
* **Last Known Working Electron version:**
  * 6.0.12

### Expected Behavior
dialog.showOpenDialog() should have the default label "Open"
dialog.showSaveDialog() should have the default label "Save"

### Actual Behavior
The labels are erroneously switched.

### Screenshots
<!-- If applicable, add screenshots to help explain your problem. -->
![labels_wrong](https://user-images.githubusercontent.com/14349333/67726433-c03fb500-f9dd-11e9-8a8a-63626e7bde1f.png)

shell/browser/ui/file_dialog_gtk.cc
#include <memory>
#include "shell/browser/ui/file_dialog.h"
#include "shell/browser/ui/gtk_util.h"
#include "base/callback.h"
#include "base/files/file_util.h"
#include "base/strings/string_util.h"
#include "chrome/browser/ui/libgtkui/gtk_util.h"
#include "shell/browser/native_window_views.h"
#include "shell/browser/unresponsive_suppressor.h"
#include "shell/common/gin_converters/file_path_converter.h"
#include "ui/base/glib/glib_signal.h"
#include "ui/views/widget/desktop_aura/x11_desktop_handler.h"
namespace file_dialog {
DialogSettings::DialogSettings() = default;
DialogSettings::DialogSettings(const DialogSettings&) = default;
DialogSettings::~DialogSettings() = default;
namespace {
static const int kPreviewWidth = 256;
static const int kPreviewHeight = 512;
gboolean FileFilterCaseInsensitive(const GtkFileFilterInfo* file_info,