net/http: update bundled http2

Updates x/net/http2 to git rev 31df19d6 for changes since Go 1.6.

The main change was https://go-review.googlesource.com/19726 (move
merging of HEADERS and CONTINUATION into Framer), but there were a few
garbage reduction changes too.

Change-Id: I882443d20749f8638f637a2835efe92538c95d31
Reviewed-on: https://go-review.googlesource.com/21365
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

src/vendor/golang.org/x/net/http2/hpack/encode.go

@@ -144,7 +144,7 @@ func (e *Encoder) SetMaxDynamicTableSizeLimit(v uint32) {
 
 // shouldIndex reports whether f should be indexed.
 func (e *Encoder) shouldIndex(f HeaderField) bool {
-	return !f.Sensitive && f.size() <= e.dynTab.maxSize
+	return !f.Sensitive && f.Size() <= e.dynTab.maxSize
 }
 
 // appendIndexed appends index i, as encoded in "Indexed Header Field"

src/vendor/golang.org/x/net/http2/hpack/hpack.go

@@ -41,6 +41,14 @@ type HeaderField struct {
 	Sensitive bool
 }
 
+// IsPseudo reports whether the header field is an http2 pseudo header.
+// That is, it reports whether it starts with a colon.
+// It is not otherwise guaranteed to be a valid psuedo header field,
+// though.
+func (hf HeaderField) IsPseudo() bool {
+	return len(hf.Name) != 0 && hf.Name[0] == ':'
+}
+
 func (hf HeaderField) String() string {
 	var suffix string
 	if hf.Sensitive {
@@ -49,7 +57,8 @@ func (hf HeaderField) String() string {
 	return fmt.Sprintf("header field %q = %q%s", hf.Name, hf.Value, suffix)
 }
 
-func (hf *HeaderField) size() uint32 {
+// Size returns the size of an entry per RFC 7540 section 5.2.
+func (hf HeaderField) Size() uint32 {
 	// http://http2.github.io/http2-spec/compression.html#rfc.section.4.1
 	// "The size of the dynamic table is the sum of the size of
 	// its entries.  The size of an entry is the sum of its name's
@@ -171,7 +180,7 @@ func (dt *dynamicTable) setMaxSize(v uint32) {
 
 func (dt *dynamicTable) add(f HeaderField) {
 	dt.ents = append(dt.ents, f)
-	dt.size += f.size()
+	dt.size += f.Size()
 	dt.evict()
 }
 
@@ -179,7 +188,7 @@ func (dt *dynamicTable) add(f HeaderField) {
 func (dt *dynamicTable) evict() {
 	base := dt.ents // keep base pointer of slice
 	for dt.size > dt.maxSize {
-		dt.size -= dt.ents[0].size()
+		dt.size -= dt.ents[0].Size()
 		dt.ents = dt.ents[1:]
 	}