Add fence support for TransferBuffers

tools/gpu/GrTest.cpp

Index: tools/gpu/GrTest.cpp
diff --git a/tools/gpu/GrTest.cpp b/tools/gpu/GrTest.cpp
index b99cf06d60a00408f3a6cfc8cfa304c6a4e93875..2e1790251948c52c98a203a4ea3803f9e853c149 100644
--- a/tools/gpu/GrTest.cpp
+++ b/tools/gpu/GrTest.cpp
@@ -318,6 +318,10 @@ public:
 
     void drawDebugWireRect(GrRenderTarget*, const SkIRect&, GrColor) override {}
 
+    GrFence SK_WARN_UNUSED_RESULT insertFence() const override { return 0; }
+    bool waitFence(GrFence, uint64_t) const override { return true; }
+    void deleteFence(GrFence) const override {}
+
 private:
     void onResetContext(uint32_t resetBits) override {}