Reduce absolute paths in generated ninja files

chrome/renderer/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/features.gni")
 import("//chrome/common/features.gni")
 import("//components/spellcheck/spellcheck_build_features.gni")
 import("//extensions/features/features.gni")
 import("//media/media_options.gni")
 import("//ppapi/features/features.gni")
 import("//tools/grit/grit_rule.gni")
 
 grit("resources") {
   source = "resources/renderer_resources.grd"
   defines = chrome_grit_defines
   output_dir = "$root_gen_dir/chrome"
   output_name = "renderer_resources"
   outputs = [
     "grit/renderer_resources.h",
     "renderer_resources_100_percent.pak",
     "renderer_resources_200_percent.pak",
     "renderer_resources_300_percent.pak",
   ]
   grit_flags = [
     "-E",
-    "mojom_root=" + rebase_path(root_gen_dir),
+    "mojom_root=" + rebase_path(root_gen_dir, root_build_dir),
   ]
   deps = [
     "//chrome/common/media_router/mojo:media_controller__generator",
     "//chrome/common/media_router/mojo:media_router__generator",
     "//mojo/common:common_custom_types__generator",
     "//net/interfaces:interfaces__generator",
     "//url/mojo:url_mojom_gurl__generator",
     "//url/mojo:url_mojom_origin__generator",
   ]
 }
@@ skipping 388 matching lines @@
     ]
   }
 
   if (is_android) {
     sources -= [
       "safe_browsing/mock_feature_extractor_clock.cc",
       "safe_browsing/mock_feature_extractor_clock.h",
     ]
   }
 }