Reduced memory footprint of QGraphicsWidget.

This commit reduces the memory footprint of QGraphicsWidget by
around 40% (from around 663 bytes to around 409 bytes - measured
using /proc/<pid>/statm on Linux - see 'man 5 proc').

The technique used is to lazily allocate (on the heap) certain
data structures (i.e. not allocate them unless they are needed):

  - QGraphicsLayoutItemPrivate::userSizeHints
    => used only if the size, width, or height is explicitly set

  - QGraphicsWidgetPrivate::margins
    => used only if the contents margins are accessed

  - QGraphicsWidgetPrivate::windowFrameMargins
    => used only if the window frame margins are accessed

  - QGraphicsWidgetPrivate::windowData
    => used only if the graphics widget is a window

In addition, a few unused data members (and related code) were removed:

  - QGraphicsWidgetPrivate::contentsRect
  - QGraphicsWidgetPrivate::mouseDelta
  - QGraphicsWidgetPrivate::*LayoutItemMargin

Reviewed-by: andreas
Task-number: 251592

0 files changed, 0 insertions, 0 deletions