Animometer: update FPS calculation

Change-Id: Idd173038505ce0af388a1fad2add673a40e6b0bf
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/132760
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Peng Huang <penghuang@chromium.org>

src/dawn/samples/Animometer.cpp

@@ -190,7 +190,8 @@ int main(int argc, const char* argv[]) {
         frameCount++;
         frame();
         if (frameCount % 60 == 0) {
-            printf("FPS: %lf\n", static_cast<double>(frameCount) / timer->GetElapsedTime());
+            printf("FPS: %lf\n", 60.0 / timer->GetElapsedTime());
+            timer->Start();
         }
     }
 }