LibCore: Add ElapsedTimer::reset()

Userland/Libraries/LibCore/ElapsedTimer.cpp

@@ -28,6 +28,12 @@ void ElapsedTimer::start()
     m_origin_time.tv_usec = now_spec.tv_nsec / 1000;
 }
 
+void ElapsedTimer::reset()
+{
+    m_valid = false;
+    m_origin_time = { 0, 0 };
+}
+
 int ElapsedTimer::elapsed() const
 {
     VERIFY(is_valid());

Userland/Libraries/LibCore/ElapsedTimer.h

@@ -22,6 +22,7 @@ public:
 
     bool is_valid() const { return m_valid; }
     void start();
+    void reset();
     int elapsed() const;
     Time elapsed_time() const;