Don't show the MDI children implicitly by default in wxMSW any more.

We kept doing it for compatibility with pre-2.5.3 versions but this was a long
time ago and we don't need this any longer.

See #2508.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75944 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/mdi.h

@@ -225,7 +225,6 @@ protected:
     void Init();
 
 private:
-    bool m_needsInitialShow; // Show must be called in idle time after Creation
     bool m_needsResize; // flag which tells us to artificially resize the frame
 
     DECLARE_EVENT_TABLE()

src/msw/mdi.cpp

@@ -757,7 +757,6 @@ bool wxMDIParentFrame::MSWTranslateMessage(WXMSG* msg)
 void wxMDIChildFrame::Init()
 {
     m_needsResize = true;
-    m_needsInitialShow = true;
 }
 
 bool wxMDIChildFrame::Create(wxMDIParentFrame *parent,
@@ -881,8 +880,6 @@ wxMDIChildFrame::~wxMDIChildFrame()
 
 bool wxMDIChildFrame::Show(bool show)
 {
-    m_needsInitialShow = false;
-
     if (!wxFrame::Show(show))
         return false;
 
@@ -1395,16 +1392,6 @@ void wxMDIClientWindow::DoSetSize(int x, int y, int width, int height, int sizeF
 
 void wxMDIChildFrame::OnIdle(wxIdleEvent& event)
 {
-    // wxMSW prior to 2.5.3 created MDI child frames as visible, which resulted
-    // in flicker e.g. when the frame contained controls with non-trivial
-    // layout. Since 2.5.3, the frame is created hidden as all other top level
-    // windows. In order to maintain backward compatibility, the frame is shown
-    // in OnIdle, unless Show(false) was called by the programmer before.
-    if ( m_needsInitialShow )
-    {
-        Show(true);
-    }
-
     // MDI child frames get their WM_SIZE when they're constructed but at this
     // moment they don't have any children yet so all child windows will be
     // positioned incorrectly when they are added later - to fix this, we