Clean up type usage and fix MSVC "truncated value" warnings in net/quic/.

net/quic/quic_stream_sequencer.cc

Index: net/quic/quic_stream_sequencer.cc
diff --git a/net/quic/quic_stream_sequencer.cc b/net/quic/quic_stream_sequencer.cc
index 5df81e5dfc02cb89afa9939c40b5b6fdc4b0e981..153e6cfb93cd041bb7bd38568a0a7bea49e267a6 100644
--- a/net/quic/quic_stream_sequencer.cc
+++ b/net/quic/quic_stream_sequencer.cc
@@ -160,7 +160,7 @@ int QuicStreamSequencer::Readv(const struct iovec* iov, size_t iov_len) {
   size_t iov_index = 0;
   size_t iov_offset = 0;
   size_t frame_offset = 0;
-  size_t initial_bytes_consumed = num_bytes_consumed_;
+  QuicStreamOffset initial_bytes_consumed = num_bytes_consumed_;
 
   while (iov_index < iov_len &&
          it != buffered_frames_.end() &&
@@ -194,7 +194,7 @@ int QuicStreamSequencer::Readv(const struct iovec* iov, size_t iov_len) {
     buffered_frames_.erase(buffered_frames_.begin());
     RecordBytesConsumed(frame_offset);
   }
-  return num_bytes_consumed_ - initial_bytes_consumed;
+  return static_cast<int>(num_bytes_consumed_ - initial_bytes_consumed);
 }
 
 bool QuicStreamSequencer::HasBytesToRead() const {