Add GrGpu support for Vulkan command buffer flush

src/gpu/GrDrawTarget.cpp

Index: src/gpu/GrDrawTarget.cpp
diff --git a/src/gpu/GrDrawTarget.cpp b/src/gpu/GrDrawTarget.cpp
index b9dc7945262056e753bf2b274d8573cef7ed6787..0173d3ba190f98914b6e0bab9ce210b7ebfa7344 100644
--- a/src/gpu/GrDrawTarget.cpp
+++ b/src/gpu/GrDrawTarget.cpp
@@ -214,7 +214,7 @@ void GrDrawTarget::drawBatches(GrBatchFlushState* flushState) {
         fBatches[i]->draw(flushState);
     }
 
-    fGpu->performFlushWorkaround();
+    fGpu->finishDrawTarget();
 }
 
 void GrDrawTarget::reset() {