cmd/internal/browser: wait 3 seconds for non-zero exit codes

Wait a short period between trying commands. Many commands
will return a non-zero exit code if the browser couldn't be launched.

For example, google-chrome returns quickly with a non-zero
exit code in a headless environment.

Updates #19131.

Change-Id: I0ae5356dd4447969d9e216615449cead7a8fd5c9
Reviewed-on: https://go-review.googlesource.com/37391Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/cmd/internal/browser/browser.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"os/exec"
 	"runtime"
+	"time"
 )
 
 // Commands returns a list of possible commands to use to open a url.
@@ -41,9 +42,26 @@ func Commands() [][]string {
 func Open(url string) bool {
 	for _, args := range Commands() {
 		cmd := exec.Command(args[0], append(args[1:], url)...)
-		if cmd.Start() == nil {
+		if cmd.Start() == nil && appearsSuccessful(cmd, 3*time.Second) {
 			return true
 		}
 	}
 	return false
 }
+
+// appearsSuccessful reports whether the command appears to have run succesfully.
+// If the command runs longer than the timeout, it's deemed successful.
+// If the command runs within the timeout, it's deemed successful if it exited cleanly.
+func appearsSuccessful(cmd *exec.Cmd, timeout time.Duration) bool {
+	errc := make(chan error, 1)
+	go func() {
+		errc <- cmd.Wait()
+	}()
+
+	select {
+	case <-time.After(timeout):
+		return true
+	case err := <-errc:
+		return err == nil
+	}
+}