Make the Device ref the Instance

This is needed before supporting instances, adapters, and devices on
the wire so that the client cannot free the instance before the device.

In Dawn native, the developer still needs to make sure the device is not
freed before all child objects.

Bug: dawn:384
Change-Id: I863d44c6a8acecc7b8ea0cc0ac483f7a864162fd
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/37003
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/Device.cpp

@@ -84,7 +84,7 @@ namespace dawn_native {
     // DeviceBase
 
     DeviceBase::DeviceBase(AdapterBase* adapter, const DeviceDescriptor* descriptor)
-        : mAdapter(adapter) {
+        : mInstance(adapter->GetInstance()), mAdapter(adapter) {
         if (descriptor != nullptr) {
             ApplyToggleOverrides(descriptor);
             ApplyExtensions(descriptor);
@@ -94,8 +94,7 @@ namespace dawn_native {
         SetDefaultToggles();
     }
 
-    DeviceBase::~DeviceBase() {
-    }
+    DeviceBase::~DeviceBase() = default;
 
     MaybeError DeviceBase::Initialize(QueueBase* defaultQueue) {
         mDefaultQueue = AcquireRef(defaultQueue);

src/dawn_native/Device.h

@@ -364,6 +364,11 @@ namespace dawn_native {
         wgpu::DeviceLostCallback mDeviceLostCallback = nullptr;
         void* mDeviceLostUserdata = nullptr;
 
+        // The Device keeps a ref to the Instance so that any live Device keeps the Instance alive.
+        // The Instance shouldn't need to ref child objects so this shouldn't introduce ref cycles.
+        // The Device keeps a simple pointer to the Adapter because the Adapter is owned by the
+        // Instance.
+        Ref<InstanceBase> mInstance;
         AdapterBase* mAdapter = nullptr;
 
         Ref<ErrorScope> mRootErrorScope;