internal/impl: change Go representation of extension lists to []T

Change-Id: Iebcefe0330c8f858c7735f9362abfd87043ee39d
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/192458
Reviewed-by: Joe Tsai <joetsai@google.com>
diff --git a/internal/impl/legacy_test.go b/internal/impl/legacy_test.go
index 08daace..3ff3f3c 100644
--- a/internal/impl/legacy_test.go
+++ b/internal/impl/legacy_test.go
@@ -392,16 +392,16 @@
 		7:  m1a,
 		8:  EnumProto2(0xbeef),
 		9:  m2a,
-		10: &[]bool{true},
-		11: &[]int32{-1000},
-		12: &[]uint32{1280},
-		13: &[]float32{1.6180},
-		14: &[]string{"zero"},
-		15: &[][]byte{[]byte("zero")},
-		16: &[]proto2_20180125.Message_ChildEnum{proto2_20180125.Message_BRAVO},
-		17: &[]*proto2_20180125.Message_ChildMessage{m1b},
-		18: &[]EnumProto2{0xdead},
-		19: &[]*EnumMessages{m2b},
+		10: []bool{true},
+		11: []int32{-1000},
+		12: []uint32{1280},
+		13: []float32{1.6180},
+		14: []string{"zero"},
+		15: [][]byte{[]byte("zero")},
+		16: []proto2_20180125.Message_ChildEnum{proto2_20180125.Message_BRAVO},
+		17: []*proto2_20180125.Message_ChildMessage{m1b},
+		18: []EnumProto2{0xdead},
+		19: []*EnumMessages{m2b},
 	}
 	for i, xt := range extensionTypes {
 		m.Set(xt.TypeDescriptor(), xt.ValueOf(setValues[i]))
@@ -423,16 +423,16 @@
 		7:  m1a,
 		8:  EnumProto2(0xbeef),
 		9:  m2a,
-		10: &[]bool{true, false},
-		11: &[]int32{-1000, -54321},
-		12: &[]uint32{1280, 6400},
-		13: &[]float32{1.6180, 2.71828},
-		14: &[]string{"zero", "goodbye, \"world!\"\n"},
-		15: &[][]byte{[]byte("zero"), []byte("live\xde\xad\xbe\xefchicken")},
-		16: &[]proto2_20180125.Message_ChildEnum{proto2_20180125.Message_BRAVO, proto2_20180125.Message_CHARLIE},
-		17: &[]*proto2_20180125.Message_ChildMessage{m1b, m1a},
-		18: &[]EnumProto2{0xdead, 0xbeef},
-		19: &[]*EnumMessages{m2b, m2a},
+		10: []bool{true, false},
+		11: []int32{-1000, -54321},
+		12: []uint32{1280, 6400},
+		13: []float32{1.6180, 2.71828},
+		14: []string{"zero", "goodbye, \"world!\"\n"},
+		15: [][]byte{[]byte("zero"), []byte("live\xde\xad\xbe\xefchicken")},
+		16: []proto2_20180125.Message_ChildEnum{proto2_20180125.Message_BRAVO, proto2_20180125.Message_CHARLIE},
+		17: []*proto2_20180125.Message_ChildMessage{m1b, m1a},
+		18: []EnumProto2{0xdead, 0xbeef},
+		19: []*EnumMessages{m2b, m2a},
 	}
 	for i, xt := range extensionTypes {
 		xd := xt.TypeDescriptor()