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/tools/quic_client_test.cc b/quic/tools/quic_client_test.cc
index 7977f05..12a687c 100644
--- a/quic/tools/quic_client_test.cc
+++ b/quic/tools/quic_client_test.cc
@@ -24,8 +24,8 @@
 
 const char* kPathToFds = "/proc/self/fd";
 
-QuicString ReadLink(const QuicString& path) {
-  QuicString result(PATH_MAX, '\0');
+std::string ReadLink(const std::string& path) {
+  std::string result(PATH_MAX, '\0');
   ssize_t result_size = readlink(path.c_str(), &result[0], result.size());
   CHECK(result_size > 0 && static_cast<size_t>(result_size) < result.size());
   result.resize(result_size);
@@ -44,7 +44,7 @@
       continue;
     }
 
-    QuicString fd_path = ReadLink(QuicStrCat(kPathToFds, "/", name));
+    std::string fd_path = ReadLink(QuicStrCat(kPathToFds, "/", name));
     if (QuicTextUtils::StartsWith(fd_path, "socket:")) {
       socket_count++;
     }