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

src/gpu/gl/GrGLGpu.cpp

Index: src/gpu/gl/GrGLGpu.cpp
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index acc2e31e88f3463a167d100ab72e2474e548005d..b6add43b2398bd110164f66ccf3f2d956a8b068b 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -4532,7 +4532,7 @@ void GrGLGpu::xferBarrier(GrRenderTarget* rt, GrXferBarrierType type) {
 }
 
 GrBackendObject GrGLGpu::createTestingOnlyBackendTexture(void* pixels, int w, int h,
-                                                         GrPixelConfig config) {
+                                                         GrPixelConfig config, bool /*isRT*/) {
     if (!this->caps()->isConfigTexturable(config)) {
         return false;
     }