dawn_wire: Add Reserve/InjectDevice

Now that the wire does enough tracking to prevent a malicious client
from freeing a device before its child objects, and the device is no
longer a "special" object with regard to reference/release, it is
safe to support multiple devices on the wire. The simplest way to
use this in WebGPU (to fix createReadyRenderPipeline validation)
is to add a reserve/inject device API similar to the one we use for
swapchain textures.

Bug: dawn:565
Change-Id: Ie956aff528c5610c9ecc5c189dab2d22185cb572
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/37800
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/include/dawn_wire/WireClient.h

@@ -38,6 +38,12 @@ namespace dawn_wire {
         uint32_t deviceGeneration;
     };
 
+    struct ReservedDevice {
+        WGPUDevice device;
+        uint32_t id;
+        uint32_t generation;
+    };
+
     struct DAWN_WIRE_EXPORT WireClientDescriptor {
         CommandSerializer* serializer;
         client::MemoryTransferService* memoryTransferService = nullptr;
@@ -53,6 +59,7 @@ namespace dawn_wire {
                                             size_t size) override final;
 
         ReservedTexture ReserveTexture(WGPUDevice device);
+        ReservedDevice ReserveDevice();
 
         // Disconnects the client.
         // Commands allocated after this point will not be sent.

src/include/dawn_wire/WireServer.h

@@ -50,6 +50,17 @@ namespace dawn_wire {
                            uint32_t deviceId = 1,
                            uint32_t deviceGeneration = 0);
 
+        bool InjectDevice(WGPUDevice device, uint32_t id, uint32_t generation);
+
+        // Look up a device by (id, generation) pair. Returns nullptr if the generation
+        // has expired or the id is not found.
+        // The Wire does not have destroy hooks to allow an embedder to observe when an object
+        // has been destroyed, but in Chrome, we need to know the list of live devices so we
+        // can call device.Tick() on all of them periodically to ensure progress on asynchronous
+        // work is made. Getting this list can be done by tracking the (id, generation) of
+        // previously injected devices, and observing if GetDevice(id, generation) returns non-null.
+        WGPUDevice GetDevice(uint32_t id, uint32_t generation);
+
       private:
         std::unique_ptr<server::Server> mImpl;
     };