Add exvar.FuncInt for exporting indirect integer variables.

R=r
APPROVED=r
DELTA=21  (21 added, 0 deleted, 0 changed)
OCL=29320
CL=29338

src/lib/exvar/exvar.go

@@ -128,6 +128,14 @@ func (v *String) Set(value string) {
 	v.s = value;
 }
 
+// IntFunc wraps a func() int64 to create a value that satisfies the Var interface.
+// The function will be called each time the Var is evaluated.
+type IntFunc func() int64;
+
+func (v IntFunc) String() string {
+	return strconv.Itoa64(v())
+}
+
 
 // All published variables.
 var vars map[string] Var = make(map[string] Var);

src/lib/exvar/exvar_test.go

@@ -78,3 +78,16 @@ func TestMapCounter(t *testing.T) {
 		t.Error("red = %v, want 3", x)
 	}
 }
+
+func TestIntFunc(t *testing.T) {
+	x := int(4);
+	ix := IntFunc(func() int64 { return int64(x) });
+	if s := ix.String(); s != "4" {
+		t.Errorf("ix.String() = %v, want 4", s);
+	}
+
+	x++;
+	if s := ix.String(); s != "5" {
+		t.Errorf("ix.String() = %v, want 5", s);
+	}
+}