Simplify changing window styles in wxMSW code

Add wxMSWWinStyleUpdater and wxMSWWinExStyleUpdater helper classes which
allow writing code changing GWL_STYLE and GWL_EXSTYLE bits,
respectively, in a shorter and more clear way.

There should be no real changes in behaviour.

include/wx/msw/private/winstyle.h

@@ -0,0 +1,134 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/msw/private/winstyle.h
+// Purpose:     Small helper class for updating MSW windows style
+// Author:      Vadim Zeitlin
+// Created:     2017-12-09
+// Copyright:   (c) 2017 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_MSW_PRIVATE_WINSTYLE_H_
+#define _WX_MSW_PRIVATE_WINSTYLE_H_
+
+// ----------------------------------------------------------------------------
+// wxMSWWinLongUpdater
+// ----------------------------------------------------------------------------
+
+/*
+    This class is not used directly, but either as wxMSWWinStyleUpdater or
+    wxMSWWinExStyleUpdater, both of which inherit from it and can be used like
+    this:
+
+    void SomeFunction()
+    {
+        wxMSWWinStyleUpdater updateStyle(GetHwndOf(m_win));
+        if ( some-condition )
+            updateStyle.TurnOn(XX_YYY);
+
+        // Style update happens here implicitly -- or call Apply().
+    }
+ */
+class wxMSWWinLongUpdater
+{
+public:
+    // Get the current style.
+    LONG_PTR Get() const
+    {
+        return m_styleCurrent;
+    }
+
+    // Check if the given style bit(s) is (are all) currently turned on.
+    bool IsOn(LONG_PTR style) const
+    {
+        return (m_styleCurrent & style) == style;
+    }
+
+    // Turn on some bit(s) in the style.
+    wxMSWWinLongUpdater& TurnOn(LONG_PTR on)
+    {
+        m_style |= on;
+        return *this;
+    }
+
+    // Turn off some bit(s) in the style.
+    wxMSWWinLongUpdater& TurnOff(LONG_PTR off)
+    {
+        m_style &= ~off;
+        return *this;
+    }
+
+    // Turn some bit(s) on or off depending on the condition.
+    wxMSWWinLongUpdater& TurnOnOrOff(bool cond, LONG_PTR style)
+    {
+        return cond ? TurnOn(style) : TurnOff(style);
+    }
+
+    // Perform the style update (only if necessary, i.e. if the style really
+    // changed).
+    //
+    // Notice that if this method is not called, it's still done from the dtor,
+    // so it's just a convenient way to do it sooner and avoid having to create
+    // a new scope for ensuring that the dtor runs at the right place, but
+    // otherwise is equivalent to do this.
+    bool Apply()
+    {
+        if ( m_style == m_styleCurrent )
+            return false;
+
+        ::SetWindowLongPtr(m_hwnd, m_gwlSlot, m_style);
+
+        m_styleCurrent = m_style;
+
+        return true;
+    }
+
+    ~wxMSWWinLongUpdater()
+    {
+        Apply();
+    }
+
+protected:
+    // Create the object for updating the style or extended style of the given
+    // window.
+    //
+    // Ctor is protected, this class can only be used as wxMSWWinStyleUpdater
+    // or wxMSWWinExStyleUpdater.
+    wxMSWWinLongUpdater(HWND hwnd, int gwlSlot)
+        : m_hwnd(hwnd),
+          m_gwlSlot(gwlSlot),
+          m_styleCurrent(::GetWindowLongPtr(hwnd, gwlSlot)),
+          m_style(m_styleCurrent)
+    {
+    }
+
+private:
+    const HWND m_hwnd;
+    const int m_gwlSlot;
+
+    LONG_PTR m_styleCurrent;
+    LONG_PTR m_style;
+
+    wxDECLARE_NO_COPY_CLASS(wxMSWWinLongUpdater);
+};
+
+// A variant of wxMSWWinLongUpdater which updates the extended style.
+class wxMSWWinStyleUpdater : public wxMSWWinLongUpdater
+{
+public:
+    explicit wxMSWWinStyleUpdater(HWND hwnd)
+        : wxMSWWinLongUpdater(hwnd, GWL_STYLE)
+    {
+    }
+};
+
+// A variant of wxMSWWinLongUpdater which updates the extended style.
+class wxMSWWinExStyleUpdater : public wxMSWWinLongUpdater
+{
+public:
+    explicit wxMSWWinExStyleUpdater(HWND hwnd)
+        : wxMSWWinLongUpdater(hwnd, GWL_EXSTYLE)
+    {
+    }
+};
+
+#endif // _WX_MSW_PRIVATE_WINSTYLE_H_