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/BUILD.gn b/BUILD.gn
index 2897286..14b9cf6 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1057,6 +1057,7 @@
     public_configs = [ ":skia_public" ]
 
     sources = [
+      "tools/SkSharingProc.cpp",
       "tools/UrlDataManager.cpp",
       "tools/debugger/DebugCanvas.cpp",
       "tools/debugger/DrawCommand.cpp",
@@ -1597,6 +1598,7 @@
       "tools/LsanSuppressions.cpp",
       "tools/ProcStats.cpp",
       "tools/Resources.cpp",
+      "tools/SkSharingProc.cpp",
       "tools/ToolUtils.cpp",
       "tools/UrlDataManager.cpp",
       "tools/debugger/DebugCanvas.cpp",