Adds support to the PacketDroppingTestWriter for dropping the first N

net/tools/quic/test_tools/packet_dropping_test_writer.h

Index: net/tools/quic/test_tools/packet_dropping_test_writer.h
diff --git a/net/tools/quic/test_tools/packet_dropping_test_writer.h b/net/tools/quic/test_tools/packet_dropping_test_writer.h
index e181fdbfcd8001598af7c8cff5f680c6f4249b93..ae1aac009cd36c378241c74e5715e4efd1b57a87 100644
--- a/net/tools/quic/test_tools/packet_dropping_test_writer.h
+++ b/net/tools/quic/test_tools/packet_dropping_test_writer.h
@@ -69,6 +69,13 @@ class PacketDroppingTestWriter : public QuicPacketWriterWrapper {
     fake_packet_loss_percentage_ = fake_packet_loss_percentage;
   }
 
+  // Simulate dropping the first n packets unconditionally.
+  // Subsequent packets will be lost at fake_packet_loss_percentage_ if set.
+  void set_fake_drop_first_n_packets(int32 fake_drop_first_n_packets) {
+    base::AutoLock locked(config_mutex_);
+    fake_drop_first_n_packets_ = fake_drop_first_n_packets;
+  }
+
   // The percent of time WritePacket will block and set WriteResult's status
   // to WRITE_STATUS_BLOCKED.
   void set_fake_blocked_socket_percentage(
@@ -141,9 +148,11 @@ class PacketDroppingTestWriter : public QuicPacketWriterWrapper {
   // Stored packets delayed by fake packet delay or bandwidth restrictions.
   DelayedPacketList delayed_packets_;
   QuicByteCount cur_buffer_size_;
+  uint64 num_calls_to_write_;
 
   base::Lock config_mutex_;
   int32 fake_packet_loss_percentage_;
+  int32 fake_drop_first_n_packets_;
   int32 fake_blocked_socket_percentage_;
   int32 fake_packet_reorder_percentage_;
   QuicTime::Delta fake_packet_delay_;