Revert "viz: DCHECK that clients don't send empty frames"

This reverts commit b44653f9.

Reason for revert: Broke the tree due to a typo :(

Original change's description:
> viz: DCHECK that clients don't send empty frames
> 
> The service rejects a CompostiorFrame if it has an empty render pass
> list, or an empty output rect.  Add a DCHECK to ensure that clients
> don't send these.
> 
> Change-Id: I2a1a25fab8b2e01f5355eaf0378c98d730490863
> Reviewed-on: https://chromium-review.googlesource.com/c/1335268
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Reviewed-by: Fady Samuel <fsamuel@chromium.org>
> Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#608087}

TBR=dcheng@chromium.org,fsamuel@chromium.org,sunnyps@chromium.org

Change-Id: I95c5f1a54a39f5ae482aa311caaf0c5fdc8df094
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/1336207Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608099}

services/viz/public/cpp/compositing/compositor_frame_struct_traits.h

@@ -28,8 +28,6 @@ struct StructTraits<viz::mojom::CompositorFrameDataView, viz::CompositorFrame> {
   }
 
   static const viz::RenderPassList& passes(const viz::CompositorFrame& input) {
-    DCHECK(!input_render_pass_list.empty());
-    DCHECK(!input.render_pass_list.back()->output_rect.size().IsEmpty());
     return input.render_pass_list;
   }