Add golang.org/x/net/http2 to the dependencies

vendor/golang.org/x/net/http2/flow.go

@@ -0,0 +1,50 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Flow control
+
+package http2
+
+// flow is the flow control window's size.
+type flow struct {
+	// n is the number of DATA bytes we're allowed to send.
+	// A flow is kept both on a conn and a per-stream.
+	n int32
+
+	// conn points to the shared connection-level flow that is
+	// shared by all streams on that conn. It is nil for the flow
+	// that's on the conn directly.
+	conn *flow
+}
+
+func (f *flow) setConnFlow(cf *flow) { f.conn = cf }
+
+func (f *flow) available() int32 {
+	n := f.n
+	if f.conn != nil && f.conn.n < n {
+		n = f.conn.n
+	}
+	return n
+}
+
+func (f *flow) take(n int32) {
+	if n > f.available() {
+		panic("internal error: took too much")
+	}
+	f.n -= n
+	if f.conn != nil {
+		f.conn.n -= n
+	}
+}
+
+// add adds n bytes (positive or negative) to the flow control window.
+// It returns false if the sum would exceed 2^31-1.
+func (f *flow) add(n int32) bool {
+	remain := (1<<31 - 1) - f.n
+	if n > remain {
+		return false
+	}
+	f.n += n
+	return true
+}