GN: Don't depend on dart_bootstrap if there is a usable prebuilt sdk

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("../../utils/invoke_dart.gni")
+import("../../build/executable_suffix.gni")
+import("../../build/prebuilt_dart_sdk.gni")
 
 config("libdart_vm_config") {
   if (defined(is_fuchsia) && is_fuchsia) {
     libs = [ "magenta" ]
   } else if (is_win) {
     libs = [
       "advapi32.lib",
       "shell32.lib",
       "dbghelp.lib",
     ]
@@ skipping 417 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 = [ "../bin:dart_bootstrap($host_toolchain)" ] +
-             concatenation_target_names
+      deps = concatenation_target_names
+      if (!prebuilt_dart_exe_works) {
+        deps += [ "../bin:dart_bootstrap($host_toolchain)" ]
+      }
 
       patches_dir = "$target_gen_dir/patches"
       patched_sdk_dir = "$root_out_dir/patched_sdk"
 
       script = "../../tools/patch_sdk.py"
 
       # We list 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($host_toolchain)",
-                                    "root_out_dir")
-      dart_bootstrap =
-          rebase_path("$dart_out_dir/dart_bootstrap$dart_executable_suffix")
-
-      args = [
-        "--dart-executable",
-        dart_bootstrap,
+      args = []
+      if (!prebuilt_dart_exe_works) {
+        dart_out_dir = get_label_info("../bin:dart_bootstrap($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),
       ]
     }
   }
 
   generate_patched_sdk("patched_sdk") {
     libraries = [
@@ skipping 41 matching lines @@
         "lib",
         "vmservice",
       ],
       [
         "bin",
         "io",
       ],
     ]
   }
 }