[url] Reserve space for "scheme://host/" for SchemeHostPort serialization

url/scheme_host_port.cc

Index: url/scheme_host_port.cc
diff --git a/url/scheme_host_port.cc b/url/scheme_host_port.cc
index 5b359a76aa4508d3783bec421110113482fe68e0..0fe87c50f9862c86f7d1af4bd9bec53ddb65ef8d 100644
--- a/url/scheme_host_port.cc
+++ b/url/scheme_host_port.cc
@@ -202,6 +202,9 @@ std::string SchemeHostPort::SerializeInternal(url::Parsed* parsed) const {
   if (IsInvalid())
     return result;
 
+  // Reserve enough space for the "normal" case of scheme://host/.
+  result.reserve(scheme_.size() + host_.size() + 4);
+
   if (!scheme_.empty()) {
     parsed->scheme = Component(0, scheme_.length());
     result.append(scheme_);