runtime: fix block profile for sync semaphores

And add a test.

LGTM=rsc
R=golang-codereviews
CC=golang-codereviews, khr, rsc
https://golang.org/cl/128670043

src/pkg/runtime/pprof/pprof_test.go

@@ -314,6 +314,12 @@ func TestBlockProfile(t *testing.T) {
 #	0x[0-9,a-f]+	sync\.\(\*Mutex\)\.Lock\+0x[0-9,a-f]+	.*/src/pkg/sync/mutex\.go:[0-9]+
 #	0x[0-9,a-f]+	runtime/pprof_test\.blockMutex\+0x[0-9,a-f]+	.*/src/pkg/runtime/pprof/pprof_test.go:[0-9]+
 #	0x[0-9,a-f]+	runtime/pprof_test\.TestBlockProfile\+0x[0-9,a-f]+	.*/src/pkg/runtime/pprof/pprof_test.go:[0-9]+
+`},
+		{"cond", blockCond, `
+[0-9]+ [0-9]+ @ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+
+#	0x[0-9,a-f]+	sync\.\(\*Cond\)\.Wait\+0x[0-9,a-f]+	.*/src/pkg/sync/cond\.go:[0-9]+
+#	0x[0-9,a-f]+	runtime/pprof_test\.blockCond\+0x[0-9,a-f]+	.*/src/pkg/runtime/pprof/pprof_test.go:[0-9]+
+#	0x[0-9,a-f]+	runtime/pprof_test\.TestBlockProfile\+0x[0-9,a-f]+	.*/src/pkg/runtime/pprof/pprof_test.go:[0-9]+
 `},
 	}
 
@@ -401,3 +407,17 @@ func blockMutex() {
 	}()
 	mu.Lock()
 }
+
+func blockCond() {
+	var mu sync.Mutex
+	c := sync.NewCond(&mu)
+	mu.Lock()
+	go func() {
+		time.Sleep(blockDelay)
+		mu.Lock()
+		c.Signal()
+		mu.Unlock()
+	}()
+	c.Wait()
+	mu.Unlock()
+}