Metal: re-enable retained references.

A client of Flutter is seeing a crash when trying to release the
MTLTexture in GrMtlAttachment. The range of CLs involved includes the
one that disables retained references in the command buffer, so this
is a speculative change to see if that is the culprit.

Change-Id: Idd6e6b264086d671be52f456ef56f1fc5bafade8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/444498
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
(cherry picked from commit 79ff8f20bf26452fd5f0a1357861ebc103a86ab6)
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/446179
Auto-Submit: Jim Van Verth <jvanverth@google.com>

src/gpu/mtl/GrMtlCommandBuffer.h

diff --git a/src/gpu/mtl/GrMtlCommandBuffer.h b/src/gpu/mtl/GrMtlCommandBuffer.h
index f18bd88..8b32974 100644
--- a/src/gpu/mtl/GrMtlCommandBuffer.h
+++ b/src/gpu/mtl/GrMtlCommandBuffer.h
@@ -51,8 +51,9 @@
     }
 
     void addResource(sk_sp<const GrManagedResource> resource) {
-        SkASSERT(resource);
-        fTrackedResources.push_back(std::move(resource));
+// Disable generic resource tracking for now
+//        SkASSERT(resource);
+//        fTrackedResources.push_back(std::move(resource));
     }
 
     void addGrBuffer(sk_sp<const GrBuffer> buffer) {

src/gpu/mtl/GrMtlCommandBuffer.mm

diff --git a/src/gpu/mtl/GrMtlCommandBuffer.mm b/src/gpu/mtl/GrMtlCommandBuffer.mm
index 255f856..0f5a0f7 100644
--- a/src/gpu/mtl/GrMtlCommandBuffer.mm
+++ b/src/gpu/mtl/GrMtlCommandBuffer.mm
@@ -22,7 +22,7 @@
 
 sk_sp<GrMtlCommandBuffer> GrMtlCommandBuffer::Make(id<MTLCommandQueue> queue) {
     id<MTLCommandBuffer> mtlCommandBuffer;
-    mtlCommandBuffer = [queue commandBufferWithUnretainedReferences];
+    mtlCommandBuffer = [queue commandBuffer];
     if (nil == mtlCommandBuffer) {
         return nullptr;
     }