json: accept escaped slash in string scanner

R=rsc
CC=golang-dev
https://golang.org/cl/1173041

src/pkg/json/decode_test.go

@@ -24,6 +24,7 @@ var unmarshalTests = []unmarshalTest{
 	unmarshalTest{`1.2`, new(float), 1.2},
 	unmarshalTest{`-5`, new(int16), int16(-5)},
 	unmarshalTest{`"a\u1234"`, new(string), "a\u1234"},
+	unmarshalTest{`"http:\/\/"`, new(string), "http://"},
 	unmarshalTest{`"g-clef: \uD834\uDD1E"`, new(string), "g-clef: \U0001D11E"},
 	unmarshalTest{`"invalid: \uD834x\uDD1E"`, new(string), "invalid: \uFFFDx\uFFFD"},
 	unmarshalTest{"null", new(interface{}), nil},

src/pkg/json/scanner.go

@@ -349,7 +349,7 @@ func stateInString(s *scanner, c int) int {
 // stateInStringEsc is the state after reading `"\` during a quoted string.
 func stateInStringEsc(s *scanner, c int) int {
 	switch c {
-	case 'b', 'f', 'n', 'r', 't', '\\', '"':
+	case 'b', 'f', 'n', 'r', 't', '\\', '/', '"':
 		s.step = stateInString
 		return scanContinue
 	}