[fiddle] Add simple animation support.

BUG=skia:

Change-Id: I6453afb1fe18e210d3c505b56777b8b19501ca2f
Reviewed-on: https://skia-review.googlesource.com/13810
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 85ae068..75a5d10 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -778,7 +778,9 @@
         "tools/fiddle/draw.cpp",
         "tools/fiddle/fiddle_main.cpp",
       ]
+      testonly = true
       deps = [
+        ":flags",
         ":skia",
         ":skia.h",
       ]