Move vulkan external commandbuffer logic from RT to GrVkFramebufer.

Bug: skia:11809
Change-Id: I7fa364f7472be35e02b06fa2f3fbb6d61a427f65
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/396156
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/GrProxyProvider.cpp b/src/gpu/GrProxyProvider.cpp
index 08d0964..1b25b06 100644
--- a/src/gpu/GrProxyProvider.cpp
+++ b/src/gpu/GrProxyProvider.cpp
@@ -658,8 +658,8 @@
 
     GrColorType colorType = SkColorTypeToGrColorType(imageInfo.colorType());
 
-    if (!this->caps()->isFormatAsColorTypeRenderable(colorType, rt->backendFormat(),
-                                                     rt->numSamples())) {
+    if (!this->caps()->isFormatAsColorTypeRenderable(
+            colorType, GrBackendFormat::MakeVk(vkInfo.fFormat), /*sampleCount=*/1)) {
         return nullptr;
     }