[sksg] Cache transformed TrimEffect geometry

Apply the effect at revalidation time, and cache the result.

TBR=

Change-Id: I166fc0e4e2869bea51e5e45e5a2a50df2f034691
Reviewed-on: https://skia-review.googlesource.com/112801
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/experimental/sksg/geometry/SkSGTrimEffect.h b/experimental/sksg/geometry/SkSGTrimEffect.h
index e86ede8..4e950a7 100644
--- a/experimental/sksg/geometry/SkSGTrimEffect.h
+++ b/experimental/sksg/geometry/SkSGTrimEffect.h
@@ -44,6 +44,7 @@
 
     const sk_sp<GeometryNode> fChild;
 
+    SkPath                    fTrimmedPath;
     SkScalar                  fStart  = 0, // starting t
                               fEnd    = 1, // ending t
                               fOffset = 0; // t offset