Subclass GrVkCommandBuffer into Primary and Secondary CommandBuffers.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2019723002

Review-Url: https://codereview.chromium.org/2019723002
diff --git a/src/gpu/vk/GrVkGpu.cpp b/src/gpu/vk/GrVkGpu.cpp
index fb533e3..d18481c 100644
--- a/src/gpu/vk/GrVkGpu.cpp
+++ b/src/gpu/vk/GrVkGpu.cpp
@@ -128,7 +128,7 @@
 
     // must call this after creating the CommandPool
     fResourceProvider.init();
-    fCurrentCmdBuffer = fResourceProvider.createCommandBuffer();
+    fCurrentCmdBuffer = fResourceProvider.createPrimaryCommandBuffer();
     SkASSERT(fCurrentCmdBuffer);
     fCurrentCmdBuffer->begin(this);
 }
@@ -169,7 +169,7 @@
 
     // Release old command buffer and create a new one
     fCurrentCmdBuffer->unref(this);
-    fCurrentCmdBuffer = fResourceProvider.createCommandBuffer();
+    fCurrentCmdBuffer = fResourceProvider.createPrimaryCommandBuffer();
     SkASSERT(fCurrentCmdBuffer);
 
     fCurrentCmdBuffer->begin(this);