Initial Lottie loader impl (Skotty)

Coarse workflow:

* Construction

  1) build a Json tree
  2) collect asset IDs (for preComp/image layer resolution)
  3) "attach" pass
     - traverse the Json tree
     - build an SkSG dom, one fragment at a time
     - attach "animator" objects to the dom, for each animated prop
  4) done, we can throw away the Json tree

* For each animation tick

  1) iterate over active animators and poke their respective dom nodes/attributes
  2) revalidate the SkSG dom
  3) draw the SkSG dom

Note: post construction, things are super-simple - we just poke SkSG DOM attributes
with interpolated values, and everything else is handled by SkSG (invalidation,
revalidation, render).

Change-Id: I96a02be7eb4fb4cb3831f59bf2b3908ea190c0dd
Reviewed-on: https://skia-review.googlesource.com/89420
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 31537cf..a61bff7 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1320,6 +1320,21 @@
     ]
   }
 
+  test_lib("experimental_skotty") {
+    public_include_dirs = [ "experimental/skotty" ]
+    include_dirs = [ "tools" ]
+    sources = [
+      "experimental/skotty/Skotty.cpp",
+      "experimental/skotty/SkottyAnimator.cpp",
+      "experimental/skotty/SkottyProperties.cpp",
+    ]
+    deps = [
+      ":experimental_sksg",
+      ":skia",
+      "//third_party/jsoncpp",
+    ]
+  }
+
   test_lib("experimental_svg_model") {
     public_include_dirs = [ "experimental/svg/model" ]
     sources = [
@@ -1877,6 +1892,7 @@
         "tools/viewer/ImageSlide.cpp",
         "tools/viewer/SKPSlide.cpp",
         "tools/viewer/SampleSlide.cpp",
+        "tools/viewer/SkottySlide.cpp",
         "tools/viewer/StatsLayer.cpp",
         "tools/viewer/Viewer.cpp",
       ]
@@ -1884,6 +1900,7 @@
 
       include_dirs = []
       deps = [
+        ":experimental_skotty",
         ":flags",
         ":gm",
         ":gpu_tool_utils",