Optimize: NativePath remembers the current work path

Rather than always querying the path with QDir::currentPath() (which
looks somewhat inefficient in the profiler), remember which path
has been set as the current path.

doomsday/libdeng2/include/de/filesys/nativepath.h

@@ -147,6 +147,15 @@ class DENG2_PUBLIC NativePath : public Path
      * Returns the current native working path.
      */
     static NativePath workPath();
+
+    /**
+     * Sets the current native working path.
+     *
+     * @param cwd  Working path.
+     *
+     * @return  @c true iff successfully changed the current working path.
+     */
+    static bool setWorkPath(NativePath const &cwd);
 };
 
 } // namespace de

doomsday/libdeng2/src/core/app.cpp

@@ -287,7 +287,7 @@ NativePath App::currentWorkPath()
 
 bool App::setCurrentWorkPath(NativePath const &cwd)
 {
-    return QDir::setCurrent(cwd);
+    return NativePath::setWorkPath(cwd);
 }
 
 NativePath App::nativeBasePath()

doomsday/libdeng2/src/filesys/nativepath.cpp

@@ -218,9 +218,25 @@ bool NativePath::exists() const
     return QFile::exists(toString());
 }
 
+static NativePath currentNativeWorkPath;
+
 NativePath NativePath::workPath()
 {
-    return QDir::currentPath();
+    if(currentNativeWorkPath.isEmpty())
+    {
+        currentNativeWorkPath = QDir::currentPath();
+    }
+    return currentNativeWorkPath;
 }
 
+bool NativePath::setWorkPath(const NativePath &cwd)
+{
+    if(QDir::setCurrent(cwd))
+    {
+        currentNativeWorkPath = cwd;
+        return true;
+    }
+    return false;
 }
+
+} // namespace de