Add Gio app shells and platform stubs (T-003)

app-win7/platform/windows/platform_test.go

@@ -0,0 +1,13 @@
+package windows
+
+import "testing"
+
+func TestPlatformStubContract(t *testing.T) {
+	platform := New()
+	if platform.OS() == "" {
+		t.Fatal("OS() should not be empty")
+	}
+	if platform.Edition() != EditionLegacy {
+		t.Fatalf("Edition() = %q, want %q", platform.Edition(), EditionLegacy)
+	}
+}