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_encrypter_test.cc b/quic/core/crypto/chacha20_poly1305_encrypter_test.cc
index d8c27bf..05f8274 100644
--- a/quic/core/crypto/chacha20_poly1305_encrypter_test.cc
+++ b/quic/core/crypto/chacha20_poly1305_encrypter_test.cc
@@ -90,15 +90,15 @@
   ChaCha20Poly1305Encrypter encrypter;
   ChaCha20Poly1305Decrypter decrypter;
 
-  QuicString key = QuicTextUtils::HexDecode(test_vectors[0].key);
+  std::string key = QuicTextUtils::HexDecode(test_vectors[0].key);
   ASSERT_TRUE(encrypter.SetKey(key));
   ASSERT_TRUE(decrypter.SetKey(key));
   ASSERT_TRUE(encrypter.SetNoncePrefix("abcd"));
   ASSERT_TRUE(decrypter.SetNoncePrefix("abcd"));
 
   uint64_t packet_number = UINT64_C(0x123456789ABC);
-  QuicString associated_data = "associated_data";
-  QuicString plaintext = "plaintext";
+  std::string associated_data = "associated_data";
+  std::string plaintext = "plaintext";
   char encrypted[1024];
   size_t len;
   ASSERT_TRUE(encrypter.EncryptPacket(packet_number, associated_data, plaintext,
@@ -114,12 +114,12 @@
 TEST_F(ChaCha20Poly1305EncrypterTest, Encrypt) {
   for (size_t i = 0; test_vectors[i].key != nullptr; i++) {
     // Decode the test vector.
-    QuicString key = QuicTextUtils::HexDecode(test_vectors[i].key);
-    QuicString pt = QuicTextUtils::HexDecode(test_vectors[i].pt);
-    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);
+    std::string key = QuicTextUtils::HexDecode(test_vectors[i].key);
+    std::string pt = QuicTextUtils::HexDecode(test_vectors[i].pt);
+    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);
 
     ChaCha20Poly1305Encrypter encrypter;
     ASSERT_TRUE(encrypter.SetKey(key));