Have gpu createTestingOlyBackendTexture know if it is a render target or not

tools/gpu/GrTest.cpp

Index: tools/gpu/GrTest.cpp
diff --git a/tools/gpu/GrTest.cpp b/tools/gpu/GrTest.cpp
index dca47baea5750e8952443ffe9e8825ed9fa6a706..d8afc820400dc76b657450cd7adaef8ccffa78a8 100644
--- a/tools/gpu/GrTest.cpp
+++ b/tools/gpu/GrTest.cpp
@@ -371,7 +371,7 @@ private:
     void clearStencil(GrRenderTarget* target) override  {}
 
     GrBackendObject createTestingOnlyBackendTexture(void* pixels, int w, int h,
-                                                    GrPixelConfig config) override {
+                                                    GrPixelConfig config, bool isRT) override {
         return 0;
     }
     bool isTestingOnlyBackendTexture(GrBackendObject ) const override { return false; }