Add support for building patched_sdk and platform.dill for dart2js:

utils/compiler/BUILD.gn

 # Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 import("../../build/compiled_action.gni")
+import("../../build/prebuilt_dart_sdk.gni")
 import("../create_timestamp.gni")
 import("../application_snapshot.gni")
 
 create_timestamp_file("dart2js_files_stamp") {
   path = rebase_path("../../pkg/compiler/lib")
   output = "$target_gen_dir/dart2js_files.stamp"
 }
 
 create_timestamp_file("runtime_lib_files_stamp") {
   path = rebase_path("../../runtime/lib")
@@ skipping 52 matching lines @@
   ]
 }
 
 application_snapshot("utils_wrapper") {
   deps = [
     ":dart2js_create_snapshot_entries",
   ]
   main_dart = "$target_gen_dir/utils_wrapper.dart"
   training_args = [ "--help" ]
 }
+
+action("patched_dart2js_sdk") {

[Vyacheslav Egorov (Google), 2017/04/27 14:07:23]

It might be a good idea to move all shared GN rules for creating patched sdk
into a template:

template("patched_sdk") {
  // ...
}

then use it here and in the VM BUILD.gn:

patched_sdk("patched_dart2js_sdk") {
  deps = [...] 
  patches_dir = "..."
  patched_sdk_dir = "..."
}

[Siggi Cherem (dart-lang), 2017/04/28 21:37:21]

Done.

+  deps = ["../../runtime/vm:patched_sdk"]
+  if (!prebuilt_dart_exe_works) {
+    deps += ["../../runtime/bin:dart_bootstrap($host_toolchain)"]
+  }
+
+  patches_dir = "../../sdk/lib/_internal/js_runtime/lib"
+  patched_sdk_dir = "$root_out_dir/patched_dart2js_sdk"
+
+  script = "../../tools/patch_sdk.py"
+
+  # We list the `patch_sdk.dart` tool here because the [script] (which is
+  # implicitly an input) will call it.
+  inputs = [
+    "../../tools/patch_sdk.dart",
+  ]
+  depfile = "$root_out_dir/patched_dart2js_sdk.d"
+
+  outputs = [
+    # Instead of listing all outputs we list a single well-known one.
+    "${patched_sdk_dir}/platform.dill",
+  ]
+
+  args = [ "--quiet" ]
+  if (!prebuilt_dart_exe_works) {
+    dart_out_dir = get_label_info(
+        "../../runtime/bin:dart_bootstrap($host_toolchain)", "root_out_dir")
+    dart_bootstrap =
+        rebase_path("$dart_out_dir/dart_bootstrap$executable_suffix")
+    args += [
+      "--dart-executable",
+      dart_bootstrap,
+    ]
+  }
+  args += [
+    "dart2js",
+    rebase_path("../../sdk"),
+    rebase_path(patches_dir),
+    rebase_path(patched_sdk_dir, root_build_dir),
+    rebase_path("../../.packages"),
+  ]
+}