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

runtime/vm/BUILD.gn

 # Copyright (c) 2014, 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/executable_suffix.gni")
 import("../../build/prebuilt_dart_sdk.gni")
+import("../../utils/generate_patch_sdk.gni")
 import("gypi_contents.gni")
 import("../runtime_args.gni")
 
 config("libdart_vm_config") {
   if (defined(is_fuchsia) && is_fuchsia) {
     libs = [ "magenta" ]
   } else if (is_win) {
     libs = [
       "advapi32.lib",
       "shell32.lib",
@@ skipping 357 matching lines @@
     inputs = []
     output = invoker.output
     script = "../tools/concatenate_patches.py"
     args = [
       "--output",
       rebase_path(output, root_build_dir),
     ]
   }
 }
 
-template("generate_patched_sdk") {
+template("generate_vm_patched_sdk") {
   assert(defined(invoker.libraries), "Need libraries in $target_name")
 
   concatenation_target_names = []
 
   # Concatenate vm library patches.
   foreach(library, invoker.libraries) {
     name = library[0]
 
     target_output = "$target_gen_dir/patches/${name}_patch.dart"
     concatenate_patch("concatenate_${name}_patch") {
       libsources = rebase_path(library[1], ".", library[2])
       output = target_output
     }
     concatenation_target_names += [ ":concatenate_${name}_patch" ]
   }
 
   # Build the patched sdk out of the concatenated patches and the special
   # libraries.
-  action(target_name) {
+  generate_patched_sdk(target_name) {
+    mode = "vm"
     deps = concatenation_target_names
-    if (!prebuilt_dart_exe_works) {
-      deps += [ "../bin:dart_bootstrap($host_toolchain)" ]
-    }
-
-    patches_dir = "$target_gen_dir/patches"
-    patched_sdk_dir = "$root_out_dir/patched_sdk"
-
-    script = "../../tools/patch_sdk.py"
-
-    # We list the `patch_sdk.dart` tool here because the [script] (which is
-    # implicitly an input) will call it.
-    inputs = [
-      "../../tools/patch_sdk.dart",
-    ]
-    depfile = "$root_out_dir/patched_sdk.d"
-
-    outputs = [
-      # Instead of listing all outputs we list a single well-known one.
-      "${patched_sdk_dir}/platform.dill",
-    ]
-
-    args = [ "--quiet" ]
-    if (!prebuilt_dart_exe_works) {
-      dart_out_dir = get_label_info("../bin:dart_bootstrap($host_toolchain)",
-                                    "root_out_dir")
-      dart_bootstrap =
-          rebase_path("$dart_out_dir/dart_bootstrap$executable_suffix")
-      args += [
-        "--dart-executable",
-        dart_bootstrap,
-      ]
-    }
-    args += [
-      "vm",
-      rebase_path("../../sdk"),
-      rebase_path(patches_dir, root_build_dir),
-      rebase_path(patched_sdk_dir, root_build_dir),
-      rebase_path("../../.packages"),
-    ]
+    input_patches_dir = "$target_gen_dir/patches"
+    patched_sdk_dir = "patched_sdk"
   }
 }
 
-generate_patched_sdk("patched_sdk") {
+generate_vm_patched_sdk("patched_sdk") {
   libraries = [
     [
       "async",
       processed_gypis.async_runtime_sources,
       "../lib",
     ],
     [
       "collection",
       processed_gypis.collection_runtime_sources,
       "../lib",
@@ skipping 48 matching lines @@
       processed_gypis.vmservice_runtime_sources,
       "../lib",
     ],
     [
       "io",
       processed_gypis.bin_io_sources,
       "../bin",
     ],
   ]
 }