If a stream is open with a HEADERS frame with no END_STREAM flag (for example, a POST request), and the server sends a response HEADERS frame with an END_STREAM flag (so that the stream gets into half closed (remote) state), then DATA frame, then the NOTREACHED() fails in spdy_stream.cc on line 524 [1]. Instead, the stream should be closed with STREAM_CLOSED:
"If an endpoint receives additional frames, other than WINDOW_UPDATE, PRIORITY, or RST_STREAM, for a stream that is in this state, it MUST respond with a stream error (Section 5.4.2) of type STREAM_CLOSED." RFC 7540 Section 7.1 [2]
[1] https://cs.chromium.org/chromium/src/net/spdy/chromium/spdy_stream.cc?q=NOTREACHED&l=524
[2] http://httpwg.org/specs/rfc7540.html#StreamStates
Comment 1 by bugdroid1@chromium.org
, Feb 9 2018