Add samples to Viewer.

This adds support with animation, assuming the sample has
implemented onAnimate. Event handling has not been
implemented.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2056343004

Committed: https://skia.googlesource.com/skia/+/76963e73704a42a18c29d6fbdcccb566e5c67658
Review-Url: https://codereview.chromium.org/2056343004
diff --git a/tools/viewer/Slide.h b/tools/viewer/Slide.h
index cdc225b..bc0ffd4 100644
--- a/tools/viewer/Slide.h
+++ b/tools/viewer/Slide.h
@@ -19,11 +19,13 @@
 public:
     virtual ~Slide() {}
 
-    virtual SkISize getDimensions() const = 0;
+    virtual SkISize getDimensions() const {
+        return SkISize::Make(0, 0);
+    }
 
     virtual void draw(SkCanvas* canvas) = 0;
     virtual bool animate(const SkAnimTimer&) { return false;  }
-    virtual void load() {}
+    virtual void load(SkScalar winWidth, SkScalar winHeight) {}
     virtual void unload() {}
 
     SkString getName() { return fName; }