Add GpuCommandBuffer support.

tools/gpu/GrTest.cpp

Index: tools/gpu/GrTest.cpp
diff --git a/tools/gpu/GrTest.cpp b/tools/gpu/GrTest.cpp
index 8fdab2e71613c899a38066119e7a8d8b932b099d..883ea56ee186a6cd2e996d10987f15d40822359f 100644
--- a/tools/gpu/GrTest.cpp
+++ b/tools/gpu/GrTest.cpp
@@ -301,6 +301,14 @@ public:
         return false;
     }
 
+    GrGpuCommandBuffer* createCommandBuffer(const GrRenderTarget& target,
+                                            GrGpuCommandBuffer::LoadAndStoreOp colorOp,
+                                            GrColor colorClear,
+                                            GrGpuCommandBuffer::LoadAndStoreOp stencilOp,
+                                            GrColor stencilClear) override {
+        return nullptr;
+    }
+
     void drawDebugWireRect(GrRenderTarget*, const SkIRect&, GrColor) override {};
 
 private: