Add fence support for TransferBuffers

src/gpu/gl/GrGLGpu.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrGLGpu.h"
 #include "GrGLBuffer.h"
 #include "GrGLGLSL.h"
@@ skipping 4676 matching lines @@
         if (GR_GL_TEXTURE_EXTERNAL == glTexture->target() ||
             GR_GL_TEXTURE_RECTANGLE == glTexture->target()) {
             copyParams->fFilter = GrTextureParams::kNone_FilterMode;
             copyParams->fWidth = texture->width();
             copyParams->fHeight = texture->height();
             return true;
         }
     }
     return false;
 }
+
+GrFence SK_WARN_UNUSED_RESULT GrGLGpu::insertFence() const {
+    GrGLsync fence;
+    GL_CALL_RET(fence, FenceSync(GR_GL_SYNC_GPU_COMMANDS_COMPLETE, 0));
+    return (GrFence)fence;
+}
+
+bool GrGLGpu::waitFence(GrFence fence, uint64_t timeout) const {
+    GrGLenum result;
+    GL_CALL_RET(result, ClientWaitSync((GrGLsync)fence, GR_GL_SYNC_FLUSH_COMMANDS_BIT, timeout));
+    return (GR_GL_CONDITION_SATISFIED == result);
+}
+
+void GrGLGpu::deleteFence(GrFence fence) const {
+    GL_CALL(DeleteSync((GrGLsync)fence));
+}