Replace QuicString with std::string, pass 1

This replaces QuicString with std::string in all of the "QUIC proper".  I will
delete QuicString once all code using it is gone.

gfe-relnote: n/a (no functional change)
PiperOrigin-RevId: 237872023
Change-Id: I82de62c9855516b15039734d05155917e68ff4ee
diff --git a/quic/core/quic_stream_sequencer.h b/quic/core/quic_stream_sequencer.h
index 3feee5e..120b997 100644
--- a/quic/core/quic_stream_sequencer.h
+++ b/quic/core/quic_stream_sequencer.h
@@ -43,7 +43,7 @@
     // Called when an error has occurred which should result in the connection
     // being closed.
     virtual void CloseConnectionWithDetails(QuicErrorCode error,
-                                            const QuicString& details) = 0;
+                                            const std::string& details) = 0;
 
     // Returns the stream id of this stream.
     virtual QuicStreamId id() const = 0;
@@ -98,7 +98,7 @@
 
   // Appends all of the readable data to |buffer| and marks all of the appended
   // data as consumed.
-  void Read(QuicString* buffer);
+  void Read(std::string* buffer);
 
   // Returns true if the sequncer has bytes available for reading.
   bool HasBytesToRead() const;
@@ -153,7 +153,7 @@
   void set_stream(StreamInterface* stream) { stream_ = stream; }
 
   // Returns string describing internal state.
-  const QuicString DebugString() const;
+  const std::string DebugString() const;
 
  private:
   friend class test::QuicStreamSequencerPeer;