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/crypto/chacha20_poly1305_decrypter_test.cc b/quic/core/crypto/chacha20_poly1305_decrypter_test.cc
index 5f5ae01..d1c8d74 100644
--- a/quic/core/crypto/chacha20_poly1305_decrypter_test.cc
+++ b/quic/core/crypto/chacha20_poly1305_decrypter_test.cc
@@ -141,12 +141,12 @@
     bool has_pt = test_vectors[i].pt;
 
     // Decode the test vector.
-    QuicString key = QuicTextUtils::HexDecode(test_vectors[i].key);
-    QuicString iv = QuicTextUtils::HexDecode(test_vectors[i].iv);
-    QuicString fixed = QuicTextUtils::HexDecode(test_vectors[i].fixed);
-    QuicString aad = QuicTextUtils::HexDecode(test_vectors[i].aad);
-    QuicString ct = QuicTextUtils::HexDecode(test_vectors[i].ct);
-    QuicString pt;
+    std::string key = QuicTextUtils::HexDecode(test_vectors[i].key);
+    std::string iv = QuicTextUtils::HexDecode(test_vectors[i].iv);
+    std::string fixed = QuicTextUtils::HexDecode(test_vectors[i].fixed);
+    std::string aad = QuicTextUtils::HexDecode(test_vectors[i].aad);
+    std::string ct = QuicTextUtils::HexDecode(test_vectors[i].ct);
+    std::string pt;
     if (has_pt) {
       pt = QuicTextUtils::HexDecode(test_vectors[i].pt);
     }