Incorrect Stream.FlowControl implementation allows to send DataFrame even when window size was exhausted. HTTP/2 server must consider such behavior as PROTOCOL_ERROR and close connection.

Existing Stream.FlowControl implementation doesn't decrease amount of permits if requested amount is less than permits. That means that client may send any amount of data if data frame size less than window size.
Fix suggested.

Minor fix: there is no necessity to decrease requested buffer by 9 (header size) because of header size is not a part of flow control.

Suggested fix: http://cr.openjdk.java.net/~skuksenko/jep110/8161091/webrev.00/