Add GrGpu support for Vulkan command buffer flush

src/gpu/GrGpu.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGpu.h"
 
@@ skipping 348 matching lines @@
     }
     return false;
 }
 
 void GrGpu::resolveRenderTarget(GrRenderTarget* target) {
     SkASSERT(target);
     this->handleDirtyContext();
     this->onResolveRenderTarget(target);
 }
 
-void GrGpu::performFlushWorkaround() {
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 
 void GrGpu::draw(const DrawArgs& args, const GrVertices& vertices) {
     this->handleDirtyContext();
     if (GrXferBarrierType barrierType = args.fPipeline->xferBarrierType(*this->caps())) {
         this->xferBarrier(args.fPipeline->getRenderTarget(), barrierType);
     }
 
     GrVertices::Iterator iter;
     const GrNonInstancedVertices* verts = iter.init(vertices);
     do {
         this->onDraw(args, *verts);
         fStats.incNumDraws();
     } while ((verts = iter.next()));
 }