[MacViews] Position modal sheets using ModalDialogHost.

chrome/browser/ui/views/frame/browser_frame_mac.mm

Index: chrome/browser/ui/views/frame/browser_frame_mac.mm
diff --git a/chrome/browser/ui/views/frame/browser_frame_mac.mm b/chrome/browser/ui/views/frame/browser_frame_mac.mm
index 2d9aa266b431e81973ffbcc22024616e104a8b70..5285ebbdda4c21b849e6b9a7809e1103143ddf62 100644
--- a/chrome/browser/ui/views/frame/browser_frame_mac.mm
+++ b/chrome/browser/ui/views/frame/browser_frame_mac.mm
@@ -8,6 +8,7 @@
 #include "chrome/browser/ui/views/frame/browser_shutdown.h"
 #include "chrome/browser/ui/views/frame/browser_view.h"
 #import "chrome/browser/ui/views/frame/native_widget_mac_frameless_nswindow.h"
+#include "components/web_modal/web_contents_modal_dialog_host.h"
 #import "ui/base/cocoa/window_size_constants.h"
 
 BrowserFrameMac::BrowserFrameMac(BrowserFrame* browser_frame,
@@ -29,6 +30,17 @@ void BrowserFrameMac::OnWindowWillClose() {
   NativeWidgetMac::OnWindowWillClose();
 }
 
+int BrowserFrameMac::SheetPositionY() {
+  web_modal::WebContentsModalDialogHost* dialog_host =
+      browser_view_->GetWebContentsModalDialogHost();
+  NSView* view = dialog_host->GetHostView();
+  // Get the position of the host view relative to the window since
+  // ModalDialogHost::GetDialogPosition() is relative to the host view.
+  int host_view_y =
+      [view convertPoint:NSMakePoint(0, NSHeight([view frame])) toView:nil].y;
+  return host_view_y - dialog_host->GetDialogPosition(gfx::Size()).y();
+}
+
 void BrowserFrameMac::InitNativeWidget(
     const views::Widget::InitParams& params) {
   views::NativeWidgetMac::InitNativeWidget(params);