Convert utility process extension Unpacker IPC to mojo

extensions/common/BUILD.gn

Index: extensions/common/BUILD.gn
diff --git a/extensions/common/BUILD.gn b/extensions/common/BUILD.gn
index 97f392b9713423682f50521b2f0c95e41deee316..fcc4a1ea391cacd6b539c2b7e9add5898fd01586 100644
--- a/extensions/common/BUILD.gn
+++ b/extensions/common/BUILD.gn
@@ -19,12 +19,18 @@ source_set("common_constants") {
 if (enable_extensions) {
   mojom("mojo") {
     sources = [
+      "extension_unpacker.mojom",
       "mojo/app_window.mojom",
       "mojo/keep_alive.mojom",
     ]
+
     if (proprietary_codecs && enable_wifi_display) {
       sources += [ "mojo/wifi_display_session_service.mojom" ]
     }
+
+    public_deps = [
+      "//mojo/common:common_custom_types",
+    ]
   }
 
   # This must be a static library because extensions common depends on