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/qpack/qpack_instruction_decoder.h b/quic/core/qpack/qpack_instruction_decoder.h
index 9d674c3..49fb0cc 100644
--- a/quic/core/qpack/qpack_instruction_decoder.h
+++ b/quic/core/qpack/qpack_instruction_decoder.h
@@ -61,8 +61,8 @@
   bool s_bit() const { return s_bit_; }
   uint64_t varint() const { return varint_; }
   uint64_t varint2() const { return varint2_; }
-  const QuicString& name() const { return name_; }
-  const QuicString& value() const { return value_; }
+  const std::string& name() const { return name_; }
+  const std::string& value() const { return value_; }
 
  private:
   enum class State {
@@ -114,8 +114,8 @@
   bool s_bit_;
   uint64_t varint_;
   uint64_t varint2_;
-  QuicString name_;
-  QuicString value_;
+  std::string name_;
+  std::string value_;
   // Whether the currently decoded header name or value is Huffman encoded.
   bool is_huffman_encoded_;
   // Length of string being read into |name_| or |value_|.