Clearing backdrop_filter_bounds in DirectRenderer::DrawFrame

This should have been cleared, but wasn't. Likely the cause of
https://crbug.com/917589.

Bug: 917589
Change-Id: I68c54ea84dba60c67fea5566a057055c6349f36e
Reviewed-on: https://chromium-review.googlesource.com/c/1394085Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619657}

components/viz/service/display/direct_renderer.cc

@@ -414,6 +414,7 @@ void DirectRenderer::DrawFrame(RenderPassList* render_passes_in_draw_order,
   render_passes_in_draw_order->clear();
   render_pass_filters_.clear();
   render_pass_backdrop_filters_.clear();
+  render_pass_backdrop_filter_bounds_.clear();
 
   current_frame_valid_ = false;
 }