[skottie] Make animated image support generally available

Consolidate some helpers under skottie_utils, and update all related
tools to support animated images.

TBR=
Change-Id: If08e97143a11d9a414f3230a49ab4284c508b9d0
Reviewed-on: https://skia-review.googlesource.com/c/169342
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/public.bzl b/public.bzl
index 703f400..b360a11 100644
--- a/public.bzl
+++ b/public.bzl
@@ -662,11 +662,14 @@
 ################################################################################
 
 SKOTTIE_TOOL_INCLUDES = [
+    "modules/skottie/utils",
     "tools/flags",
 ]
 
 SKOTTIE_TOOL_SRCS = [
     "modules/skottie/src/SkottieTool.cpp",
+    "modules/skottie/utils/SkottieUtils.cpp",
+    "modules/skottie/utils/SkottieUtils.h",
     # TODO(benjaminwagner): Add "flags" target.
     "tools/flags/SkCommandLineFlags.cpp",
     "tools/flags/SkCommandLineFlags.h",