Make SkAnimTimer support speed control

Really helpful to slow down animated content for debugging, etc...

Bug: skia:
Change-Id: Id22ac555c7926dc858777d3d1be8afac1686407a
Reviewed-on: https://skia-review.googlesource.com/c/182920
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/tools/viewer/SlideDir.cpp b/tools/viewer/SlideDir.cpp
index 54db653..9be4bb5 100644
--- a/tools/viewer/SlideDir.cpp
+++ b/tools/viewer/SlideDir.cpp
@@ -82,7 +82,7 @@
 
 private:
     void tick(SkMSec t) {
-        fSlide->animate(SkAnimTimer(0, t * 1e6, SkAnimTimer::kRunning_State));
+        fSlide->animate(SkAnimTimer(t * 1e6));
         this->invalidate();
     }