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 edbf276efd3479624a13782607e64f3dc1fa85c4..b04f449edb82c578f75bbe0a2a32cfe6739f6e3c 100644
--- a/extensions/common/BUILD.gn
+++ b/extensions/common/BUILD.gn
@@ -19,11 +19,17 @@ source_set("common_constants") {
 if (enable_extensions) {
   mojom("mojo") {
     sources = [
+      "extension_unpacker.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