[release-branch.go1.7] reflect: clear tflag on new types

Fixes #16722

Change-Id: I50a0e69d3e79d13bc1860cd983267c3db087a4b8
Reviewed-on: https://go-review.googlesource.com/27119Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-on: https://go-review.googlesource.com/28630

src/reflect/all_test.go

@@ -5720,6 +5720,8 @@ func TestTypeStrings(t *testing.T) {
 		{TypeOf(new(XM)), "*reflect_test.XM"},
 		{TypeOf(new(XM).String), "func() string"},
 		{TypeOf(new(XM)).Method(0).Type, "func(*reflect_test.XM) string"},
+		{ChanOf(3, TypeOf(XM{})), "chan reflect_test.XM"},
+		{MapOf(TypeOf(int(0)), TypeOf(XM{})), "map[int]reflect_test.XM"},
 	}
 
 	for i, test := range stringTests {

src/reflect/type.go

@@ -1848,6 +1848,7 @@ func ChanOf(dir ChanDir, t Type) Type {
 	prototype := *(**chanType)(unsafe.Pointer(&ichan))
 	ch := new(chanType)
 	*ch = *prototype
+	ch.tflag = 0
 	ch.dir = uintptr(dir)
 	ch.str = resolveReflectName(newName(s, "", "", false))
 	ch.hash = fnv1(typ.hash, 'c', byte(dir))
@@ -1892,6 +1893,7 @@ func MapOf(key, elem Type) Type {
 	mt := new(mapType)
 	*mt = **(**mapType)(unsafe.Pointer(&imap))
 	mt.str = resolveReflectName(newName(s, "", "", false))
+	mt.tflag = 0
 	mt.hash = fnv1(etyp.hash, 'm', byte(ktyp.hash>>24), byte(ktyp.hash>>16), byte(ktyp.hash>>8), byte(ktyp.hash))
 	mt.key = ktyp
 	mt.elem = etyp