Add a constructor that explicitly takes a size to QLatin1String

This is useful in a couple of situations where the size is known
at runtime and one wants to avoid a call to strlen.

Change-Id: Ic20587b0d365a4573d4636c5853c206b571b8d6b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>

src/corelib/tools/qstring.cpp

@@ -7164,6 +7164,19 @@ QString &QString::setRawData(const QChar *unicode, int size)
     \sa latin1()
 */
 
+/*! \fn QLatin1String::QLatin1String(const char *str, int size)
+
+    Constructs a QLatin1String object that stores \a str with \a size.
+    Note that if \a str is 0, an empty string is created; this case
+    is handled by QString.
+
+    The string data is \e not copied. The caller must be able to
+    guarantee that \a str will not be deleted or modified as long as
+    the QLatin1String object exists.
+
+    \sa latin1()
+*/
+
 /*! \fn const char *QLatin1String::latin1() const
 
     Returns the Latin-1 string stored in this object.

src/corelib/tools/qstring.h

@@ -646,6 +646,7 @@ class QLatin1String
 {
 public:
     Q_DECL_CONSTEXPR inline explicit QLatin1String(const char *s) : m_size(s ? int(strlen(s)) : 0), m_data(s) {}
+    Q_DECL_CONSTEXPR inline explicit QLatin1String(const char *s, int size) : m_size(size), m_data(s) {}
 
     inline const char *latin1() const { return m_data; }
     inline int size() const { return m_size; }