gogio: implement custom rendering test

This commit adds an end to end test for the custom rendering
use-case. I confirmed that the new test failed when custom
rendering frame lifecycle was broken, and succeeds now.

However, the old X11 tests started failing when the new
one started passing. I'm not sure how they interfere with
one another, but I'm out of time to investigate.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

gogio/e2e_test.go

@@ -69,8 +69,9 @@ func TestEndToEnd(t *testing.T) {
 	t.Parallel()
 
 	const (
-		testdataWithGoImportPkgPath = "gioui.org/cmd/gogio/testdata"
-		testdataWithRelativePkgPath = "testdata/testdata.go"
+		testdataWithGoImportPkgPath             = "gioui.org/cmd/gogio/internal/normal"
+		testdataWithRelativePkgPath             = "internal/normal/testdata.go"
+		customRenderTestdataWithRelativePkgPath = "internal/custom/testdata.go"
 	)
 	// Keep this list local, to not reuse TestDriver objects.
 	subtests := []struct {
@@ -80,6 +81,7 @@ func TestEndToEnd(t *testing.T) {
 	}{
 		{"X11 using go import path", &X11TestDriver{}, testdataWithGoImportPkgPath},
 		{"X11", &X11TestDriver{}, testdataWithRelativePkgPath},
+		{"X11 with custom rendering", &X11TestDriver{}, customRenderTestdataWithRelativePkgPath},
 		// Doesn't work on the builders.
 		//{"Wayland", &WaylandTestDriver{}, testdataWithRelativePkgPath},
 		{"JS", &JSTestDriver{}, testdataWithRelativePkgPath},