GN: Fall back on dart_bootstrap where appropriate.

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.
 
 config("libdart_vm_config") {
   if (defined(is_fuchsia) && is_fuchsia) {
     libs = [ "magenta" ]
   } else if (is_win) {
     libs = [
       "advapi32.lib",
@@ skipping 420 matching lines @@
         dir = library[0]
         output = target_output
       }
       concatenation_target_names += [ ":concatenate_${name}_patch" ]
       concatenation_files += [ target_output ]
     }
 
     # Build the patched sdk out of the concatenated patches and the special
     # libraries.
     action(target_name) {
-      deps = concatenation_target_names
+      deps = [ "../bin:dart_bootstrap($host_toolchain)" ] +
+             concatenation_target_names
 
       patches_dir = "$target_gen_dir/patches"
       patched_sdk_dir = "$root_out_dir/patched_sdk"
 
       script = "../../tools/patch_sdk.py"
 
       # We list all files which make up the sdk (modulo patches) and get them back
       # as a GN list object.
       shared_sdk_sources = exec_script("../../tools/list_dart_files.py",
                                        [ "../../sdk/lib" ],
@@ skipping 19 matching lines @@
       inputs += shared_sdk_sources
 
       # Add all the concatenated patch files.
       inputs += concatenation_files
 
       outputs = [
         # Instead of listing all outputs we list a single well-known one.
         "${patched_sdk_dir}/lib/core/core.dart",
       ]
 
+      dart_out_dir = get_label_info("../bin:dart_bootstrap($host_toolchain)",
+                                    "root_out_dir")
+      if (is_win) {
+        dart_bootstrap = rebase_path("$dart_out_dir/dart_bootstrap.exe")

[Cutch, 2016/11/01 19:33:52]

This `if (is_win) { } else { }` pattern is repeated, is there no
$platform_executable_suffix equivalent ? Maybe add one?

[zra, 2016/11/01 19:59:28]

Added to invoke_dart.gni

+      } else {
+        dart_bootstrap = rebase_path("$dart_out_dir/dart_bootstrap")
+      }
+
       args = [
+        "--dart-executable",
+        dart_bootstrap,
         "vm",
         rebase_path("../../sdk"),
         rebase_path(patches_dir, root_build_dir),
         rebase_path(patched_sdk_dir, root_build_dir),
       ]
     }
   }
 
   generate_patched_sdk("patched_sdk") {
     libraries = [
@@ skipping 41 matching lines @@
         "lib",
         "vmservice",
       ],
       [
         "bin",
         "io",
       ],
     ]
   }
 }