gpu: Empty swaps for surfaceless output surfaces.

gpu/command_buffer/common/capabilities.h

Index: gpu/command_buffer/common/capabilities.h
diff --git a/gpu/command_buffer/common/capabilities.h b/gpu/command_buffer/common/capabilities.h
index 41ab8efd591bcd351787a12d92f5590e4cd80e45..410f65c3771a5b7bae54f118c3bb9128a544097c 100644
--- a/gpu/command_buffer/common/capabilities.h
+++ b/gpu/command_buffer/common/capabilities.h
@@ -172,6 +172,9 @@ struct GPU_EXPORT Capabilities {
   // See https://crbug.com/710029.
   bool software_to_accelerated_canvas_upgrade = true;
 
+  // When true, non-empty post sub buffer calls are unsupported.
+  bool disable_non_empty_post_sub_buffers = false;

[jbauman, 2017/04/20 00:23:47]

Wouldn't an empty PostSubBuffers with a surfaceless compositor be essentially
equal to CommitOverlayPlanes? Maybe we should just be using that instead.

[reveman, 2017/04/20 18:21:35]

Almost. We still need to commit the primary plane and not just the overlays for
now. That can change in the future as it's not a requirement at the lowest
level, I think. I can look at that as a follow up but as we need this to be
merged into M58 I'd like to first land this SwapBuffers based approach.

+
   int major_version = 2;
   int minor_version = 0;
 };