Fix debugger build by specifying nullptr for color space.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2181733002

Review-Url: https://codereview.chromium.org/2181733002
diff --git a/debugger/QT/SkGLWidget.cpp b/debugger/QT/SkGLWidget.cpp
index 975052f..57cb49d 100644
--- a/debugger/QT/SkGLWidget.cpp
+++ b/debugger/QT/SkGLWidget.cpp
@@ -63,7 +63,7 @@
     sk_sp<GrRenderTarget> curRenderTarget(
             fCurContext->textureProvider()->wrapBackendRenderTarget(desc));
     SkSurfaceProps props(0, kUnknown_SkPixelGeometry);
-    fGpuDevice.reset(SkGpuDevice::Make(std::move(curRenderTarget), &props,
+    fGpuDevice.reset(SkGpuDevice::Make(std::move(curRenderTarget), nullptr, &props,
                                        SkGpuDevice::kUninit_InitContents).release());
     fCanvas.reset(new SkCanvas(fGpuDevice));
 }