Bug 1575008 - WebGPU implementation basis r=webidl,baku

This change vendors `wgpu` library in-tree and hooks up the initialization bits. It implements adapter and device initialization and adds a simple test.

Current status:
  - [x] Architecture
    - [x] figure out the IPC story
    - [ ] move wgpu crates into a dedicated folder (let's follow up with this)
  - [x] Review
    - [x] WebIDL changes by DOM peers
  - [x] Linux
    - [x] avoid depending on spirv_cross - https://github.com/gfx-rs/wgpu/pull/371
  - [x] macOS
    - [x] due to cross-compiling shaders - https://github.com/gfx-rs/gfx/pull/3047
    - [x] need the dependency update
    - [x] stop using gcc - https://github.com/SSheldon/rust-objc-exception/pull/5
    - [x] unexpected SSL header collision - https://phabricator.services.mozilla.com/D51148
    - [x] undefined Metal symbols
    - [x] missing webrtc headers for IPDL magic - https://phabricator.services.mozilla.com/D51558
  - [x] Windows
    - [x] due to "ipc-channel" not supporting Windows yet - https://github.com/servo/ipc-channel/pull/233~~
    - [x] due to some exceptional stuff - https://github.com/grovesNL/spirv_cross/issues/121
    - [x] undefined symbol: `D3D12CreateDevice`
    - [x] d3d12.dll is not found, dxgi1_4 doesn't present
    - [x] d3d11.dll and dxgi.dll need to be explicitly loaded on win32 mingw - https://github.com/gfx-rs/gfx/pull/3076
    - [x] libbacktrace fails to link on win32 mingw
    - [x] cc mislinking C++ standard library - https://github.com/alexcrichton/cc-rs/pull/455
  - [x] Android
    - [x] spirv-cross fails to build - https://github.com/KhronosGroup/SPIRV-Cross/pull/1193

Update-1:
We decided to go with IPDL mechanism instead of Rust based ipc-channel (or any alternatives), which unblocks Windows build.

Update-2:
It appears that WebGPUThreading isn't needed any more as the child thread (and its event loop) is now managed by IPDL infrastructure. This PR removes it 🎉 .

Update-3:
InstanceProvider is also removed.

Update-4:
All set, the try is green, waiting for dependent changes to go in.

Differential Revision: https://phabricator.services.mozilla.com/D49458

dom/webgpu/Instance.cpp

@@ -6,20 +6,34 @@
 #include "Instance.h"
 
 #include "Adapter.h"
-#include "InstanceProvider.h"
+#include "gfxConfig.h"
 #include "nsIGlobalObject.h"
+#include "ipc/WebGPUChild.h"
+#include "ipc/WebGPUTypes.h"
+#include "mozilla/layers/CompositorBridgeChild.h"
 
 namespace mozilla {
 namespace webgpu {
 
-GPU_IMPL_CYCLE_COLLECTION(Instance, mParent)
+GPU_IMPL_CYCLE_COLLECTION(Instance, mOwner)
 
 /*static*/
-RefPtr<Instance> Instance::Create(nsIGlobalObject* parent) {
-  return new Instance(parent);
+RefPtr<Instance> Instance::Create(nsIGlobalObject* aOwner) {
+  if (!gfx::gfxConfig::IsEnabled(gfx::Feature::WEBGPU)) {
+    return nullptr;
+  }
+
+  RefPtr<WebGPUChild> bridge =
+      layers::CompositorBridgeChild::Get()->GetWebGPUChild();
+  if (NS_WARN_IF(!bridge)) {
+    MOZ_CRASH("Failed to create an IPDL bridge for WebGPU!");
+  }
+
+  return new Instance(aOwner, bridge);
 }
 
-Instance::Instance(nsIGlobalObject* parent) : mParent(parent) {}
+Instance::Instance(nsIGlobalObject* aOwner, WebGPUChild* aBridge)
+    : mOwner(aOwner), mBridge(aBridge) {}
 
 Instance::~Instance() = default;
 
@@ -28,5 +42,31 @@ JSObject* Instance::WrapObject(JSContext* cx,
   return dom::GPU_Binding::Wrap(cx, this, givenProto);
 }
 
+RefPtr<WebGPUChild> Instance::GetBridge() const { return mBridge; }
+
+already_AddRefed<dom::Promise> Instance::RequestAdapter(
+    const dom::GPURequestAdapterOptions& aOptions, ErrorResult& aRv) {
+  RefPtr<dom::Promise> promise = dom::Promise::Create(mOwner, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  RefPtr<Instance> instance = this;
+
+  mBridge->InstanceRequestAdapter(aOptions)->Then(
+      GetMainThreadSerialEventTarget(), __func__,
+      [promise, instance](RawId id) {
+        MOZ_ASSERT(id != 0);
+        RefPtr<Adapter> adapter = new Adapter(instance, id);
+        promise->MaybeResolve(adapter);
+      },
+      [promise](const Maybe<ipc::ResponseRejectReason>& aRv) {
+        promise->MaybeReject(aRv.isSome() ? NS_ERROR_CONNECTION_REFUSED
+                                          : NS_ERROR_FAILURE);
+      });
+
+  return promise.forget();
+}
+
 }  // namespace webgpu
 }  // namespace mozilla