message: Fix scissor rect larger than render pass width/height in Metal backend
  TEST=dawn_end2end_tests
diff: @@ -667,6 +667,15 @@ namespace dawn_native { namespace metal {
  rect.width = cmd->width;
  rect.height = cmd->height;
  + // The scissor rect x + width must be <= render pass width
  + if ((rect.x + rect.width) > renderPassCmd->width) {
  + rect.width = renderPassCmd->width - rect.x;
  + }
  + // The scissor rect y + height must be <= render pass height
  + if ((rect.y + rect.height > renderPassCmd->height)) {
  + rect.height = renderPassCmd->height - rect.y;
  + }
  +
  [encoder setScissorRect:rect];
  } break;
  