Fix the |accept_events| InitParam to work on Windows.

WS_EX_TRANSPARENT only seems to mean "pass events to the underlying window" when
the windows in question is also WS_EX_LAYERED.

Bug: 1004721
Change-Id: Ia2618ddfa9c16a49fd8eb156ab0c7793736bce0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1816745
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698569}

ui/views/widget/widget_hwnd_utils.cc

@@ -42,7 +42,7 @@ void CalculateWindowStylesFromInitParams(
   if (params.show_state == ui::SHOW_STATE_MINIMIZED)
     *style |= WS_MINIMIZE;
   if (!params.accept_events)
-    *ex_style |= WS_EX_TRANSPARENT;
+    *ex_style |= WS_EX_TRANSPARENT | WS_EX_LAYERED;
   DCHECK_NE(Widget::InitParams::ACTIVATABLE_DEFAULT, params.activatable);
   if (params.activatable == Widget::InitParams::ACTIVATABLE_NO)
     *ex_style |= WS_EX_NOACTIVATE;