Some more improvements/fixes to the VulkanViewer

tools/vulkan/viewer/VulkanViewer.h

Index: tools/vulkan/viewer/VulkanViewer.h
diff --git a/tools/vulkan/viewer/VulkanViewer.h b/tools/vulkan/viewer/VulkanViewer.h
index 29cbbef16ea08d99c2b08b03d3feefd6fe9179db..b012cf1cdde096280bdb9c6250785c4cac882aa4 100644
--- a/tools/vulkan/viewer/VulkanViewer.h
+++ b/tools/vulkan/viewer/VulkanViewer.h
@@ -22,11 +22,17 @@ public:
     bool onKey(Window::Key key, Window::InputState state, uint32_t modifiers);
     void onPaint(SkCanvas* canvas);
 
-    void onIdle(float dt) override;
+    void onIdle(double ms) override;
 
 private:
+    void drawStats(SkCanvas* canvas);
+
     Window*      fWindow;
 
+    static const int kMeasurementCount = 64;  // should be power of 2 for fast mod
+    double fMeasurements[kMeasurementCount];
+    int fCurrentMeasurement;
+
     const skiagm::GMRegistry* fGMs;
 };