Menu window should not appear in taskbar

The window of menu should have the WS_EX_TOOLWINDOW style, otherwise
when showing tray context menu on Windows, its window would show in
taskbar.

Bug: 1094772
Change-Id: If822315b6b8d7322b919fb1c5e550c96cbbdb823
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2245941Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Mason Freed <masonfreed@chromium.org>
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781667}

ui/views/widget/widget_hwnd_utils.cc

@@ -118,6 +118,8 @@ void CalculateWindowStylesFromInitParams(
         else
           *style |= WS_BORDER;
       }
+      if (!params.force_show_in_taskbar)
+        *ex_style |= WS_EX_TOOLWINDOW;
       break;
     case Widget::InitParams::TYPE_TOOLTIP:
       *style |= WS_POPUP;