Add fence support for TransferBuffers

BUG=skia:4604
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2384463003

Review-Url: https://codereview.chromium.org/2384463003
diff --git a/src/gpu/vk/GrVkCaps.cpp b/src/gpu/vk/GrVkCaps.cpp
index e72e723..d982756 100644
--- a/src/gpu/vk/GrVkCaps.cpp
+++ b/src/gpu/vk/GrVkCaps.cpp
@@ -36,6 +36,7 @@
     fOversizedStencilSupport = false; //TODO: figure this out
 
     fUseDrawInsteadOfClear = false;
+    fFenceSyncSupport = true;   // always available in Vulkan
 
     fMapBufferFlags = kNone_MapFlags; //TODO: figure this out
     fBufferMapThreshold = SK_MaxS32;  //TODO: figure this out