Add QHttpHeaders::reserve()

Found in API-review

Change-Id: Ia41eb91e9e62a252b76c20c67c1c599c0f6a633d
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit b5665f6fab40232a81a056523608c295c8167bc6)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/network/access/qhttpheaders.cpp

@@ -1063,6 +1063,18 @@ qsizetype QHttpHeaders::size() const noexcept
     return d->headers.size();
 }
 
+/*!
+    Attempts to allocate memory for at least \a size header entries.
+
+    If you know in advance how how many header entries there will
+    be, you may call this function to prevent reallocations
+    and memory fragmentation.
+*/
+void QHttpHeaders::reserve(qsizetype size)
+{
+    d->headers.reserve(size);
+}
+
 /*!
     Compares this instance with \a other and returns \c true if they
     are considered equal in accordance with the provided \a options.

src/network/access/qhttpheaders.h

@@ -247,6 +247,7 @@ public:
     Q_NETWORK_EXPORT QByteArray combinedValue(WellKnownHeader name) const;
 
     Q_NETWORK_EXPORT qsizetype size() const noexcept;
+    Q_NETWORK_EXPORT void reserve(qsizetype size);
     bool isEmpty() const noexcept { return size() == 0; }
 
     Q_NETWORK_EXPORT bool equals(const QHttpHeaders &other,