video: Added a hint to override the display's usable bounds.

include/SDL_hints.h

@@ -1229,6 +1229,20 @@ extern "C" {
  */
 #define SDL_HINT_WAVE_FACT_CHUNK   "SDL_WAVE_FACT_CHUNK"
 
+/*
+ *  \brief Override for SDL_GetDisplayUsableBounds()
+ *
+ *  If set, this hint will override the expected results for
+ *  SDL_GetDisplayUsableBounds() for display index 0. Generally you don't want
+ *  to do this, but this allows an embedded system to request that some of the
+ *  screen be reserved for other uses when paired with a well-behaved
+ *  application.
+ *
+ *  The contents of this hint must be 4 comma-separated integers, the first
+ *  is the bounds x, then y, width and height, in that order.
+ */
+#define SDL_HINT_DISPLAY_USABLE_BOUNDS "SDL_DISPLAY_USABLE_BOUNDS"
+
 /**
  *  \brief  An enumeration of hint priorities
  */