Remove Http2String wrapper for std::string.

gfe-relnote: n/a, no functional change.
PiperOrigin-RevId: 263816460
Change-Id: I4f365540414e6a3d78fd00ce6b39a4cdd4c14140
diff --git a/http2/tools/random_util.cc b/http2/tools/random_util.cc
index 82c3edd..a7d95c4 100644
--- a/http2/tools/random_util.cc
+++ b/http2/tools/random_util.cc
@@ -11,7 +11,7 @@
 
 // Here "word" means something that starts with a lower-case letter, and has
 // zero or more additional characters that are numbers or lower-case letters.
-Http2String GenerateHttp2HeaderName(size_t len, Http2Random* rng) {
+std::string GenerateHttp2HeaderName(size_t len, Http2Random* rng) {
   Http2StringPiece alpha_lc = "abcdefghijklmnopqrstuvwxyz";
   // If the name is short, just make it one word.
   if (len < 8) {
@@ -25,13 +25,13 @@
          rng->RandStringWithAlphabet(len - 4, alphanumdash_lc);
 }
 
-Http2String GenerateWebSafeString(size_t len, Http2Random* rng) {
+std::string GenerateWebSafeString(size_t len, Http2Random* rng) {
   static const char* kWebsafe64 =
       "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_";
   return rng->RandStringWithAlphabet(len, kWebsafe64);
 }
 
-Http2String GenerateWebSafeString(size_t lo, size_t hi, Http2Random* rng) {
+std::string GenerateWebSafeString(size_t lo, size_t hi, Http2Random* rng) {
   return GenerateWebSafeString(rng->UniformInRange(lo, hi), rng);
 }