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/crypto_utils_test.cc b/quic/core/crypto/crypto_utils_test.cc
index 90a37af..c76337d 100644
--- a/quic/core/crypto/crypto_utils_test.cc
+++ b/quic/core/crypto/crypto_utils_test.cc
@@ -50,18 +50,18 @@
 
   for (size_t i = 0; i < QUIC_ARRAYSIZE(test_vector); i++) {
     // Decode the test vector.
-    QuicString subkey_secret =
+    std::string subkey_secret =
         QuicTextUtils::HexDecode(test_vector[i].subkey_secret);
-    QuicString label = QuicTextUtils::HexDecode(test_vector[i].label);
-    QuicString context = QuicTextUtils::HexDecode(test_vector[i].context);
+    std::string label = QuicTextUtils::HexDecode(test_vector[i].label);
+    std::string context = QuicTextUtils::HexDecode(test_vector[i].context);
     size_t result_len = test_vector[i].result_len;
     bool expect_ok = test_vector[i].expected != nullptr;
-    QuicString expected;
+    std::string expected;
     if (expect_ok) {
       expected = QuicTextUtils::HexDecode(test_vector[i].expected);
     }
 
-    QuicString result;
+    std::string result;
     bool ok = CryptoUtils::ExportKeyingMaterial(subkey_secret, label, context,
                                                 result_len, &result);
     EXPECT_EQ(expect_ok, ok);