tools: separate TimeUtils from AnimTimer

gm, slides, and samples no longer need to know about the implementation
details of AnimTimer.

This
    virtual bool onAnimate(const AnimTimer&);
becomes this:
    virtual bool onAnimate(double /*nanoseconds*/);
which is much easier to reason about.

AnimTimer itself is now part of viewer.

Change-Id: Ib70bf7a0798b1991f25204ae84f70463cdbeb358
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/226838
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/samplecode/SampleLighting.cpp b/samplecode/SampleLighting.cpp
index 022e44d..a8bd72e 100644
--- a/samplecode/SampleLighting.cpp
+++ b/samplecode/SampleLighting.cpp
@@ -69,7 +69,7 @@
         return this->INHERITED::onFindClickHandler(x, y, modi);
     }
 
-    bool onAnimate(const AnimTimer& timer) override {
+    bool onAnimate(double nanos) override {
         fLightAngle += 0.015f;
         fColorFactor += 0.01f;
         if (fColorFactor > 1.0f) {