Enable compression of observatory_assets.tar in standalone GN build

runtime/observatory/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Currently paths here are hard coded for convenience in building Mojo/Flutter.
 declare_args() {
   # Specify the path to a host compatible version of the Dart SDK.
   # This SDK is used to compile the Observatory frontend sources.
   dart_host_sdk = rebase_path("//third_party/dart-sdk/dart-sdk")
 
@@ skipping 142 matching lines @@
   outputs = [
     "$root_out_dir/observatory/deployed/web/main.dart.js",
   ]
 }
 
 template("observatory_archive") {
   assert(defined(invoker.inner_namespace),
          "Need inner_namespace in $target_name")
   assert(defined(invoker.outer_namespace),
          "Need outer_namespace in $target_name")
+  enable_compression = false
+  if (defined(invoker.compress) && invoker.compress) {
+    enable_compression = true
+  }
   action(target_name) {
     deps = [
       ":deploy_observatory",
     ]
 
     script = "../tools/create_archive.py"
 
-  inputs = [
-    script,
-    "$root_out_dir/observatory/deployed/web/main.dart.js",
-  ]
+    inputs = [
+      script,
+      "$root_out_dir/observatory/deployed/web/main.dart.js",
+    ]
 
     inner_namespace = invoker.inner_namespace
     outer_namespace = invoker.outer_namespace
     output_name = target_name
     args = [
       "--output",
       rebase_path("$root_gen_dir/observatory/${output_name}.cc"),
       "--tar_output",
       rebase_path("$root_gen_dir/observatory/${output_name}.tar"),
       "--outer_namespace", outer_namespace,
       "--inner_namespace", inner_namespace,
       "--name", "observatory_assets_archive",
       "--client_root", rebase_path("$root_out_dir/observatory/deployed/web/"),
     ]
+    if (enable_compression) {
+      args += [ "--compress" ]
+    }
 
     outputs = [
       "$root_gen_dir/observatory/${output_name}.cc",
       "$root_gen_dir/observatory/${output_name}.tar",
     ]
   }
 }
 
 observatory_archive("embedded_archive_observatory") {
   outer_namespace = "dart"
   inner_namespace = "observatory"
 }
 
 source_set("embedded_observatory_archive") {
   deps = [
     ":embedded_archive_observatory",
   ]
 
   sources = [
     rebase_path("$root_gen_dir/observatory/embedded_archive_observatory.cc"),
   ]
 }
 
 observatory_archive("standalone_archive_observatory") {
+  compress = true
   outer_namespace = "dart"
   inner_namespace = "bin"
 }
 
 source_set("standalone_observatory_archive") {
   deps = [
     ":standalone_archive_observatory",
   ]
 
   sources = [
     rebase_path("$root_gen_dir/observatory/standalone_archive_observatory.cc"),
   ]
 }