Bug 570625, part 7: Add gfxXlibSurface::ReleasePixmap() to undo TakePixmap(). sr=roc

gfx/thebes/gfxXlibSurface.h

@@ -100,6 +100,15 @@ public:
         mPixmapTaken = PR_TRUE;
     }
 
+    // Release ownership of this surface's Pixmap.  This is only valid
+    // on gfxXlibSurfaces for which the user called TakePixmap(), or
+    // on those created by a Create() factory method.
+    Drawable ReleasePixmap() {
+        NS_ASSERTION(mPixmapTaken, "I don't own the Pixmap!");
+        mPixmapTaken = PR_FALSE;
+        return mDrawable;
+    }
+
     // Find a visual and colormap pair suitable for rendering to this surface.
     PRBool GetColormapAndVisual(Colormap* colormap, Visual **visual);