cc: Make OutputSurface::SwapBuffers pure virtual

mojo/examples/compositor_app/BUILD.gn

Index: mojo/examples/compositor_app/BUILD.gn
diff --git a/mojo/examples/compositor_app/BUILD.gn b/mojo/examples/compositor_app/BUILD.gn
deleted file mode 100644
index 8ef8ad7bd54d01f671f25818e7c614013cd30751..0000000000000000000000000000000000000000
--- a/mojo/examples/compositor_app/BUILD.gn
+++ /dev/null
@@ -1,28 +0,0 @@
-# Copyright 2014 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-# GYP version mojo/mojo_examples.gypi:mojo_compositor_app
-shared_library("compositor_app") {
-  output_name = "mojo_compositor_app"
-
-  sources = [
-    "compositor_app.cc",
-    "compositor_host.cc",
-    "compositor_host.h",
-  ]
-
-  deps = [
-    "//base",
-    "//cc",
-    "//mojo/application",
-    "//mojo/cc",
-    "//mojo/common",
-    "//mojo/public/c/system:for_shared_library",
-    "//mojo/public/gles2:for_shared_library",
-    "//mojo/services/public/cpp/geometry",
-    "//mojo/services/public/interfaces/geometry",
-    "//mojo/services/public/interfaces/gpu",
-    "//mojo/services/public/interfaces/native_viewport",
-  ]
-}