net/http: update bundled http2

Update x/net/http2 to git rev 6b17b9baf5 for:

   http2: stop rejecting outgoing paths beginning with two slashes
   https://golang.org/cl/45773

This also uses an updated version of x/tools/cmd/bundle (CL 45190)
that fixes an edge case where it used to drop some comments.

Updates #20627
Fixes #19103

Change-Id: I450d61485e66098f4f8a79954f729f7bcd85856f
Reviewed-on: https://go-review.googlesource.com/45700
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Chris Broadfoot <cbro@golang.org>

src/net/http/h2_bundle.go

@@ -48,6 +48,9 @@ import (
 	"golang_org/x/net/lex/httplex"
 )
 
+// A list of the possible cipher suite ids. Taken from
+// http://www.iana.org/assignments/tls-parameters/tls-parameters.txt
+
 const (
 	http2cipher_TLS_NULL_WITH_NULL_NULL               uint16 = 0x0000
 	http2cipher_TLS_RSA_WITH_NULL_MD5                 uint16 = 0x0001
@@ -1206,11 +1209,16 @@ type http2goAwayFlowError struct{}
 
 func (http2goAwayFlowError) Error() string { return "connection exceeded flow control window size" }
 
+// connError represents an HTTP/2 ConnectionError error code, along
+// with a string (for debugging) explaining why.
+//
 // Errors of this type are only returned by the frame parser functions
-// and converted into ConnectionError(ErrCodeProtocol).
+// and converted into ConnectionError(Code), after stashing away
+// the Reason into the Framer's errDetail field, accessible via
+// the (*Framer).ErrorDetail method.
 type http2connError struct {
-	Code   http2ErrCode
-	Reason string
+	Code   http2ErrCode // the ConnectionError error code
+	Reason string       // additional reason
 }
 
 func (e http2connError) Error() string {
@@ -3562,14 +3570,18 @@ func (s *http2sorter) SortStrings(ss []string) {
 // validPseudoPath reports whether v is a valid :path pseudo-header
 // value. It must be either:
 //
-//     *) a non-empty string starting with '/', but not with with "//",
+//     *) a non-empty string starting with '/'
 //     *) the string '*', for OPTIONS requests.
 //
 // For now this is only used a quick check for deciding when to clean
 // up Opaque URLs before sending requests from the Transport.
 // See golang.org/issue/16847
+//
+// We used to enforce that the path also didn't start with "//", but
+// Google's GFE accepts such paths and Chrome sends them, so ignore
+// that part of the spec. See golang.org/issue/19103.
 func http2validPseudoPath(v string) bool {
-	return (len(v) > 0 && v[0] == '/' && (len(v) == 1 || v[1] != '/')) || v == "*"
+	return (len(v) > 0 && v[0] == '/') || v == "*"
 }
 
 // pipe is a goroutine-safe io.Reader/io.Writer pair. It's like
@@ -8694,7 +8706,7 @@ func (p *http2writeGoAway) writeFrame(ctx http2writeContext) error {
 	return err
 }
 
-func (*http2writeGoAway) staysWithinBuffer(max int) bool { return false }
+func (*http2writeGoAway) staysWithinBuffer(max int) bool { return false } // flushes
 
 type http2writeData struct {
 	streamID  uint32
@@ -9205,7 +9217,7 @@ func (p *http2writeQueuePool) get() *http2writeQueue {
 }
 
 // RFC 7540, Section 5.3.5: the default weight is 16.
-const http2priorityDefaultWeight = 15
+const http2priorityDefaultWeight = 15 // 16 = 15 + 1
 
 // PriorityWriteSchedulerConfig configures a priorityWriteScheduler.
 type http2PriorityWriteSchedulerConfig struct {