WebUI generator GN build file fixed.

components/webui_generator/generator/wug.gni

 # 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.
 
 # Generates native and HTML/JS supporting code for Web UI element from element's
 # declaration JSON file.
 #
 # Parameters:
 #
 #   source (required)
@@ skipping 23 matching lines @@
   src_root = rebase_path("//", root_build_dir)
 
   helper_path = "$generator_dir/build_helper.py"
   target_name = "${target_name}"
   action_name = target_name + "_gen"
   out_dir = "$root_gen_dir/wug"
 
   helper_args = [
     rebase_path(declaration_path, root_build_dir),
     "--destination",
-    out_dir,
+    rebase_path(out_dir, root_build_dir),
     "--root",
     src_root,
     "--gn",
     "--output",
   ]
 
   expected_target_name =
       exec_script(helper_path, helper_args + [ "target_name" ], "trim string")
   assert(target_name == expected_target_name,
          "Wrong target name. " + "Expected '" + expected_target_name +
@@ skipping 23 matching lines @@
       common_prefix + "view_model.h",
       common_prefix + "view_model.cc",
       common_prefix + "web_ui_view.h",
       common_prefix + "web_ui_view.cc",
     ]
     args = [
       rebase_path(declaration_path, root_build_dir),
       "--root",
       src_root,
       "--destination",
-      out_dir,
+      rebase_path(out_dir, root_build_dir),
     ]
   }
 
   component(target_name) {
     sources = get_target_outputs(":$action_name")
     defines = [ exec_script(helper_path,
                             helper_args + [ "impl_macro" ],
                             "trim string") ]
     deps = [
       "//base",
       "//components/login",
       "//components/strings",
     ]
     deps += exec_script(helper_path,
                         helper_args + [ "import_dependencies" ],
                         "list lines")
     public_deps = [
       "//components/webui_generator",
     ]
 
     all_dependent_configs =
         [ "//components/webui_generator:wug_generated_config" ]
   }
 }