QUIC/cronet - Fix crash bug b/28676259. Handle session_ being a nullptr.

net/quic/quic_http_stream.cc

Index: net/quic/quic_http_stream.cc
diff --git a/net/quic/quic_http_stream.cc b/net/quic/quic_http_stream.cc
index 803f84c7b54a8848281f520454d7d26c7f630545..78b793cbcaf3c53b91062a261c92ab3afa7bdba0 100644
--- a/net/quic/quic_http_stream.cc
+++ b/net/quic/quic_http_stream.cc
@@ -175,6 +175,12 @@ int QuicHttpStream::InitializeStream(const HttpRequestInfo* request_info,
 }
 
 int QuicHttpStream::DoStreamRequest() {
+  if (session_.get() == nullptr) {

[xunjieli, 2016/06/07 23:46:25]

Could just do "if (!session_)". It's more consistent with the other null checks
in this file.  

[ramant (doing other things), 2016/06/07 23:58:32]

Regarding WeakPtr, the following discussion could be interesting.

https://mail.google.com/mail/u/0/#search/label%3Achromium-dev+weakptr/155189b...

Wanted to see if there is a platform specific bug. Will change it to (!session_)
and will add UMA histograms to track how many times we hit this condition.

[ramant (doing other things), 2016/06/18 00:18:05]

Uploaded CL: https://codereview.chromium.org/2073323003/ to collect histogram
data.

+    // TODO(rtenneti) Bug: b/28676259 - a temporary fix until we find out why
+    // |session_| could be a nullptr.
+    return was_handshake_confirmed_ ? ERR_CONNECTION_CLOSED
+                                    : ERR_QUIC_HANDSHAKE_FAILED;
+  }
   int rv = stream_request_.StartRequest(
       session_, &stream_,
       base::Bind(&QuicHttpStream::OnStreamReady, weak_factory_.GetWeakPtr()));