all: replace InvalidateOp with InvalidateCmd command

Curiously, InvalidateCmd is probably the only command that is appropriate
to call during layout.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

io/input/router_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"gioui.org/io/pointer"
+	"gioui.org/op"
 )
 
 func TestNoFilterAllocs(t *testing.T) {
@@ -22,3 +23,12 @@ func TestNoFilterAllocs(t *testing.T) {
 		t.Fatalf("expected 0 AllocsPerOp, got %d", allocs)
 	}
 }
+
+func TestRouterWakeup(t *testing.T) {
+	r := new(Router)
+	r.Source().Execute(op.InvalidateCmd{})
+	r.Frame(new(op.Ops))
+	if _, wake := r.WakeupTime(); !wake {
+		t.Errorf("InvalidateCmd did not trigger a redraw")
+	}
+}