Remove inability to call QuicSimpleServerPacketWriter::WritePacket directly.

Fixes toy server crash described here:
https://groups.google.com/a/chromium.org/forum/#!topic/proto-quic/ziwUgZbV2Wk

BUG=

Review-Url: https://codereview.chromium.org/2180003004
Cr-Commit-Position: refs/heads/master@{#408221}

net/tools/quic/quic_simple_server_packet_writer.cc

@@ -45,7 +45,9 @@ void QuicSimpleServerPacketWriter::OnWriteComplete(int rv) {
   DCHECK_NE(rv, ERR_IO_PENDING);
   write_blocked_ = false;
   WriteResult result(rv < 0 ? WRITE_STATUS_ERROR : WRITE_STATUS_OK, rv);
-  base::ResetAndReturn(&callback_).Run(result);
+  if (!callback_.is_null()) {
+    base::ResetAndReturn(&callback_).Run(result);
+  }
   blocked_writer_->OnCanWrite();
 }
 
@@ -71,7 +73,6 @@ WriteResult QuicSimpleServerPacketWriter::WritePacket(
   scoped_refptr<StringIOBuffer> buf(
       new StringIOBuffer(std::string(buffer, buf_len)));
   DCHECK(!IsWriteBlocked());
-  DCHECK(!callback_.is_null());
   int rv;
   if (buf_len <= static_cast<size_t>(std::numeric_limits<int>::max())) {
     rv = socket_->SendTo(

net/tools/quic/quic_simple_server_packet_writer.h

@@ -33,15 +33,19 @@ class QuicSimpleServerPacketWriter : public QuicPacketWriter {
                                QuicBlockedWriterInterface* blocked_writer);
   ~QuicSimpleServerPacketWriter() override;
 
-  // Use this method to write packets rather than WritePacket:
-  // QuicSimpleServerPacketWriter requires a callback to exist for every
-  // write, which will be called once the write completes.
-  virtual WriteResult WritePacketWithCallback(const char* buffer,
-                                              size_t buf_len,
-                                              const IPAddress& self_address,
-                                              const IPEndPoint& peer_address,
-                                              PerPacketOptions* options,
-                                              WriteCallback callback);
+  // Wraps WritePacket, and ensures that |callback| is run on successful write.
+  WriteResult WritePacketWithCallback(const char* buffer,
+                                      size_t buf_len,
+                                      const IPAddress& self_address,
+                                      const IPEndPoint& peer_address,
+                                      PerPacketOptions* options,
+                                      WriteCallback callback);
+
+  WriteResult WritePacket(const char* buffer,
+                          size_t buf_len,
+                          const IPAddress& self_address,
+                          const IPEndPoint& peer_address,
+                          PerPacketOptions* options) override;
 
   void OnWriteComplete(int rv);
 
@@ -51,14 +55,6 @@ class QuicSimpleServerPacketWriter : public QuicPacketWriter {
   void SetWritable() override;
   QuicByteCount GetMaxPacketSize(const IPEndPoint& peer_address) const override;
 
- protected:
-  // Do not call WritePacket on its own -- use WritePacketWithCallback
-  WriteResult WritePacket(const char* buffer,
-                          size_t buf_len,
-                          const IPAddress& self_address,
-                          const IPEndPoint& peer_address,
-                          PerPacketOptions* options) override;
-
  private:
   UDPServerSocket* socket_;