test: apply GO_TEST_TIMEOUT_SCALE scaling to test timeouts

Change run.go to apply the GO_TEST_TIMEOUT_SCALE scaling factor to
test timeouts (mentioned in "-t" clause in test header).

Also with this patch, bump up the timeout for fixedbugs/issue46234.go
from 30 to 45 seconds, to avoid flakes on very slow builders.

Updates #50973.

Change-Id: Icbafa482860e24cc1e72fee53511bcc764d06bf1
Reviewed-on: https://go-review.googlesource.com/c/go/+/382774
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

test/fixedbugs/issue46234.go

@@ -1,5 +1,6 @@
-// buildrun -t 30
+// buildrun -t 45
 
+//go:build !js
 // +build !js
 
 // Copyright 2021 The Go Authors. All rights reserved.

test/run.go

@@ -710,6 +710,13 @@ func (t *test) run() {
 			if err != nil {
 				t.err = fmt.Errorf("need number of seconds for -t timeout, got %s instead", args[0])
 			}
+			if s := os.Getenv("GO_TEST_TIMEOUT_SCALE"); s != "" {
+				timeoutScale, err := strconv.Atoi(s)
+				if err != nil {
+					log.Fatalf("failed to parse $GO_TEST_TIMEOUT_SCALE = %q as integer: %v", s, err)
+				}
+				tim *= timeoutScale
+			}
 		case "-goexperiment": // set GOEXPERIMENT environment
 			args = args[1:]
 			if goexp != "" {
@@ -834,6 +841,13 @@ func (t *test) run() {
 		if tim != 0 {
 			err = cmd.Start()
 			// This command-timeout code adapted from cmd/go/test.go
+			// Note: the Go command uses a more sophisticated timeout
+			// strategy, first sending SIGQUIT (if appropriate for the
+			// OS in question) to try to trigger a stack trace, then
+			// finally much later SIGKILL. If timeouts prove to be a
+			// common problem here, it would be worth porting over
+			// that code as well. See https://do.dev/issue/50973
+			// for more discussion.
 			if err == nil {
 				tick := time.NewTimer(time.Duration(tim) * time.Second)
 				done := make(chan error)