[Cronet] Use WeakPtr in CronetBidirectionalStream on iOS.

components/cronet/ios/test/cronet_bidirectional_stream_test.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import <Foundation/Foundation.h>
 #include <stdint.h>
 #include <list>
 #include <map>
 #include <string>
 
@@ skipping 149 matching lines @@
   virtual bool MaybeCancel(cronet_bidirectional_stream* stream,
                            ResponseStep step) {
     DCHECK_EQ(stream, this->stream);
     response_step = step;
     DLOG(WARNING) << "Step: " << step;
 
     if (step != cancel_from_step)
       return false;
 
     cronet_bidirectional_stream_cancel(stream);
+    cronet_bidirectional_stream_write(stream, "abc", 3, false);
+
     return true;
   }
 
   void SignalDone() { stream_done_event.Signal(); }
 
   void BlockForDone() { stream_done_event.Wait(); }
 
   void AddWriteData(const std::string& data) { AddWriteData(data, true); }
   void AddWriteData(const std::string& data, bool flush) {
     write_data.push_back(base::MakeUnique<WriteData>(data, flush));
@@ skipping 496 matching lines @@
   ASSERT_EQ(TestBidirectionalStreamCallback::ON_FAILED, test.response_step);
   ASSERT_EQ(net::ERR_NAME_NOT_RESOLVED, test.net_error);
   cronet_bidirectional_stream_destroy(test.stream);
 }
 
 INSTANTIATE_TEST_CASE_P(CronetBidirectionalStreamDelayRequestHeadersUntilFlush,
                         CronetBidirectionalStreamTest,
                         ::testing::Values(true, false));
 
 }  // namespace cronet