Perform Vulkan resets in a background thread

Bug: skia:
Change-Id: I90783dc9ac2fcae560cd54e6c8c6df11d7195ac0
Reviewed-on: https://skia-review.googlesource.com/c/168488
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/vk/GrVkSemaphore.cpp b/src/gpu/vk/GrVkSemaphore.cpp
index ef53b30..8491782 100644
--- a/src/gpu/vk/GrVkSemaphore.cpp
+++ b/src/gpu/vk/GrVkSemaphore.cpp
@@ -51,7 +51,7 @@
 
 void GrVkSemaphore::onRelease() {
     if (fResource) {
-        fResource->unref(static_cast<const GrVkGpu*>(this->getGpu()));
+        fResource->unref(static_cast<GrVkGpu*>(this->getGpu()));
         fResource = nullptr;
     }
     INHERITED::onRelease();
@@ -65,7 +65,7 @@
     INHERITED::onAbandon();
 }
 
-void GrVkSemaphore::Resource::freeGPUData(const GrVkGpu* gpu) const {
+void GrVkSemaphore::Resource::freeGPUData(GrVkGpu* gpu) const {
     if (fIsOwned) {
         GR_VK_CALL(gpu->vkInterface(),
                    DestroySemaphore(gpu->device(), fSemaphore, nullptr));