The `wgpu::Device::Tick()` function is not available when the Dawn
backend is compiled using emsdk to target WebAssembly. As an
alternative, this CL introduces code that takes advantage of
emscripten's Asyncify feature to yield execution to the browser's event
loop and allowing it to execute async tasks from blocking Skia code.
* Introduced the GrDawnAsyncWait class which abstracts over Asyncify vs
wgpu::Device::Tick depending on the platform and implements common
busy-wait boilerplate.
* Refactored the fence management in GrDawnGpu to make use of
GrDawnAsyncWait. The GPUQueue.onSubmittedWorkDone is now handled by a
callback on GrDawnGpu instead of per-fence callbacks since the latter
cannot easily prevent a use-after-free if a fence is destroyed before
the callback runs.
Bug: skia:12512
Change-Id: I255e92ec87c799dc7a50bd034a815c0aaca0ef5f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/530736
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Arman Uguray <armansito@google.com>
0c3dda058c