Reland "Deserialize MultiPictureDocument based SKP files (with image sharing proc) in wasm debugger."

This is a reland of 7635013ad16a60cfa5ff93af28c5fab8927c92ce

Original change's description:
> Deserialize MultiPictureDocument based SKP files (with image sharing proc) in wasm debugger.
> 
> Change-Id: I73affae3cd05a2aa6ac1c75c8e049d352bbf3a85
> Bug: 9176
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/217135
> Commit-Queue: Nathaniel Nifong <nifong@google.com>
> Reviewed-by: Derek Sollenberger <djsollen@google.com>
> Reviewed-by: Kevin Lubick <kjlubick@google.com>

Bug: 9176
Change-Id: Ifef1ff45ac0013ba3015f88c7ecd75527b28b604
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/222505
Commit-Queue: Nathaniel Nifong <nifong@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
diff --git a/gn/tests.gni b/gn/tests.gni
index 734c1e4..ac67998 100644
--- a/gn/tests.gni
+++ b/gn/tests.gni
@@ -152,6 +152,7 @@
   "$_tests/MessageBusTest.cpp",
   "$_tests/MetaDataTest.cpp",
   "$_tests/MipMapTest.cpp",
+  "$_tests/MultiSkpTest.cpp",
   "$_tests/NonlinearBlendingTest.cpp",
   "$_tests/OctoBoundsTest.cpp",
   "$_tests/OSPathTest.cpp",