if (mBlack)
if (mBlack && mOwnBlackSurface)
BlendingBuffers::~BlendingBuffers() {  if (mOffScreen)    mCleanupContext->DestroyDrawingSurface(mOffScreen);  if (mOffScreenWhite)    mCleanupContext->DestroyDrawingSurface(mOffScreenWhite);  if (mWhite)    mCleanupContext->DestroyDrawingSurface(mWhite);  if (mBlack)    mCleanupContext->DestroyDrawingSurface(mBlack);}