As in topic. API currently offers fixed ratio only for Mac but not for Windows
shell/browser/ui/views/frameless_view.cc
#include "shell/browser/ui/views/frameless_view.h"
#include "shell/browser/native_browser_view_views.h"
#include "shell/browser/native_window_views.h"
#include "ui/aura/window.h"
#include "ui/base/hit_test.h"
#include "ui/views/widget/widget.h"
#include "ui/views/widget/widget_delegate.h"
namespace electron {
namespace {
const int kResizeInsideBoundsSize = 5;
const int kResizeAreaCornerSize = 16;
}  
const char FramelessView::kViewClassName[] = "FramelessView";
FramelessView::FramelessView() = default;
FramelessView::~FramelessView() = default;
void FramelessView::Init(NativeWindowViews* window, views::Widget* frame) {
  window_ = window;
  frame_ = frame;
}
int FramelessView::ResizingBorderHitTest(const gfx::Point& point) {