Allow building mojo_shell and non-graphical apps/services on a Mac

ui/gl/gl_surface_mac.cc

Index: ui/gl/gl_surface_mac.cc
diff --git a/ui/gl/gl_surface_mac.cc b/ui/gl/gl_surface_mac.cc
index 28a8b8513c02405050847b2de9de391dc3e39ba2..05eb817d96b3091a4f7e5fcee6ff43a0a3d1c47e 100644
--- a/ui/gl/gl_surface_mac.cc
+++ b/ui/gl/gl_surface_mac.cc
@@ -43,9 +43,9 @@ class GL_EXPORT NoOpGLSurface : public GLSurface {
   bool Initialize() override { return true; }
   void Destroy() override {}
   bool IsOffscreen() override { return true; }
-  bool SwapBuffers() override {
+  gfx::SwapResult SwapBuffers() override {
     NOTREACHED() << "Cannot call SwapBuffers on a NoOpGLSurface.";
-    return false;
+    return gfx::SwapResult::SWAP_FAILED;
   }
   gfx::Size GetSize() override { return size_; }
   void* GetHandle() override { return NULL; }