[vr] Fix test app build.

As of crrev.com/c/741451, SwapBuffers now requires an argument.

TBR=cjgrant@chromium.org

Bug: None
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I2bc85fe0d232ca2dac3758bb1ba88d6f329f4021
Reviewed-on: https://chromium-review.googlesource.com/802018
Commit-Queue: Ian Vollick <vollick@chromium.org>
Reviewed-by: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520724}

chrome/browser/vr/testapp/gl_renderer.cc

@@ -42,7 +42,8 @@ bool GlRenderer::Initialize() {
 void GlRenderer::RenderFrame() {
   context_->MakeCurrent(surface_.get());
   vr_->DrawFrame();
-  PostRenderFrameTask(surface_->SwapBuffers());
+  PostRenderFrameTask(
+      surface_->SwapBuffers(gl::GLSurface::PresentationCallback()));
 }
 
 void GlRenderer::PostRenderFrameTask(gfx::SwapResult result) {