[ADD] Add measurement for chapters

apps/chapter_06.cpp

@@ -26,6 +26,7 @@
 // This is an independent project of an individual developer. Dear PVS-Studio, please check it.
 // PVS-Studio Static Code Analyzer for C, C++, C#, and Java: http://www.viva64.com
 
+#include <chrono>
 #include <cstdio>
 
 #include <raytracing.h>
@@ -37,6 +38,7 @@
 #define kWallZ     10
 
 using namespace Raytracer;
+using namespace std;
 
 /* ------------------------------------------------------------------------- */
 
@@ -93,6 +95,17 @@ int shadow_sphere(uint8_t a_canvas_pixels, double a_wall_size, uint8_t a_wall_z)
 
 int main(void)
 {
+    int the_ret;
+    chrono::time_point<chrono::high_resolution_clock> the_start, the_end;
+
     printf("Chapter 06 example.\n");
-    return shadow_sphere(kImageSize, kWallSize, kWallZ);
+
+    the_start = chrono::high_resolution_clock::now();
+    the_ret   = shadow_sphere(kImageSize, kWallSize, kWallZ);
+    the_end   = chrono::high_resolution_clock::now();
+
+    chrono::duration<double> the_elapsed_time = the_end - the_start;
+    printf("Execution Time: %f secondes\n", the_elapsed_time.count());
+
+    return the_ret;
 }