[Cronet] Use WeakPtr in CronetBidirectionalStream on iOS.

components/cronet/ios/cronet_bidirectional_stream.h

Index: components/cronet/ios/cronet_bidirectional_stream.h
diff --git a/components/cronet/ios/cronet_bidirectional_stream.h b/components/cronet/ios/cronet_bidirectional_stream.h
index 6d82b2327f62265ce08a9116b0534296a0b0d289..9df7de1766f55db7bca49b8e06a6a9b31c442d80 100644
--- a/components/cronet/ios/cronet_bidirectional_stream.h
+++ b/components/cronet/ios/cronet_bidirectional_stream.h
@@ -10,6 +10,7 @@
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
 #include "base/synchronization/lock.h"
 #include "net/http/bidirectional_stream.h"
 
@@ -220,6 +221,9 @@ class CronetBidirectionalStream : public net::BidirectionalStream::Delegate {
   std::unique_ptr<net::BidirectionalStream> bidi_stream_;
   Delegate* delegate_;
 
+  base::WeakPtr<CronetBidirectionalStream> weak_this_;
+  base::WeakPtrFactory<CronetBidirectionalStream> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(CronetBidirectionalStream);
 };