rate: extend timing tolerances on Android and Plan9

Fixes #43055

Change-Id: I72a88ff9d031192911a90a607eaf0366575eb313
Reviewed-on: https://go-review.googlesource.com/c/time/+/387834
Reviewed-by: Sameer Ajmani <sameer@golang.org>
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

rate/rate_test.go

diff --git a/rate/rate_test.go b/rate/rate_test.go
index 1ca3711..57dd1a7 100644
--- a/rate/rate_test.go
+++ b/rate/rate_test.go
@@ -437,10 +437,14 @@
 	// (The latter is surely less than half a d.)
 	maxD := wantD
 	switch runtime.GOOS {
-	case "netbsd", "openbsd":
+	case "netbsd", "openbsd", "android", "plan9":
 		// NetBSD and OpenBSD tend to overshoot sleeps by a wide margin due to a
 		// suspected platform bug; see https://go.dev/issue/44067 and
 		// https://go.dev/issue/50189.
+		//
+		// Android and plan9 were empirically observed to overshoot too.
+		// Android might be trying to conserve power.
+		// For plan9, I (bcmills) am not sure what the problem would be.
 		maxD = (wantD*3 + 1) / 2 // 150% of wantD, rounded up.
 	}
 	return gotD <= maxD