runtime, time: accelerate tests in short mode.

                                   before   after
go test -short time                4.144s  1.215s
go test -short runtime             1.315s  0.351s
go test -short -cpu=1,2,4 runtime  4.376s  1.266s

Partially solves issue 3015.

R=golang-dev, r
CC=golang-dev, remy
https://golang.org/cl/5673045

src/pkg/runtime/gc_test.go

@@ -15,7 +15,11 @@ func TestGcSys(t *testing.T) {
 	runtime.ReadMemStats(memstats)
 	sys := memstats.Sys
 
-	for i := 0; i < 1000000; i++ {
+	itercount := 1000000
+	if testing.Short() {
+		itercount = 100000
+	}
+	for i := 0; i < itercount; i++ {
 		workthegc()
 	}
 

src/pkg/time/sleep_test.go

@@ -108,10 +108,11 @@ func TestAfter(t *testing.T) {
 }
 
 func TestAfterTick(t *testing.T) {
-	const (
-		Delta = 100 * Millisecond
-		Count = 10
-	)
+	const Count = 10
+	Delta := 100 * Millisecond
+	if testing.Short() {
+		Delta = 10 * Millisecond
+	}
 	t0 := Now()
 	for i := 0; i < Count; i++ {
 		<-After(Delta)
@@ -176,9 +177,10 @@ func await(slot int, result chan<- afterResult, ac <-chan Time) {
 }
 
 func testAfterQueuing(t *testing.T) error {
-	const (
-		Delta = 100 * Millisecond
-	)
+	Delta := 100 * Millisecond
+	if testing.Short() {
+		Delta = 20 * Millisecond
+	}
 	// make the result channel buffered because we don't want
 	// to depend on channel queueing semantics that might
 	// possibly change in the future.

src/pkg/time/tick_test.go

@@ -10,10 +10,11 @@ import (
 )
 
 func TestTicker(t *testing.T) {
-	const (
-		Delta = 100 * Millisecond
-		Count = 10
-	)
+	const Count = 10
+	Delta := 100 * Millisecond
+	if testing.Short() {
+		Delta = 10 * Millisecond
+	}
 	ticker := NewTicker(Delta)
 	t0 := Now()
 	for i := 0; i < Count; i++ {
@@ -39,8 +40,12 @@ func TestTicker(t *testing.T) {
 
 // Test that a bug tearing down a ticker has been fixed.  This routine should not deadlock.
 func TestTeardown(t *testing.T) {
+	Delta := 100 * Millisecond
+	if testing.Short() {
+		Delta = 20 * Millisecond
+	}
 	for i := 0; i < 3; i++ {
-		ticker := NewTicker(1e8)
+		ticker := NewTicker(Delta)
 		<-ticker.C
 		ticker.Stop()
 	}