grit: Use new --write-only-new flag.

content/browser/devtools/devtools_resources.gyp

 # Copyright (c) 2012 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.
 
 {
   'targets': [
     {
       'target_name': 'devtools_resources',
       'type': 'none',
       'dependencies': [
         '../../../third_party/WebKit/public/blink_devtools.gyp:blink_generate_devtools_grd',
       ],
       'variables': {
         'grit_out_dir': '<(SHARED_INTERMEDIATE_DIR)/webkit',
       },
       'actions': [
         {
           'action_name': 'devtools_resources',
           # This can't use build/grit_action.gypi because the grd file
           # is generated at build time, so the trick of using grit_info to get
           # the real inputs/outputs at GYP time isn't possible.
           'variables': {
             'grit_cmd': ['python', '../../../tools/grit/grit.py'],
             'grit_grd_file': '<(SHARED_INTERMEDIATE_DIR)/devtools/devtools_resources.grd',
             'grit_rc_header_format%': '',
+
+            'conditions': [
+              # These scripts can skip writing generated files if they are
+              # identical to the already existing files, which avoids further
+              # build steps, like recompilation. However, a dependency (earlier
+              # build step) having a newer timestamp than an output (later
+              # build step) confuses some build systems, so only use this on
+              # ninja, which explicitly supports this use case (gyp turns all
+              # actions into ninja restat rules).
+              ['"<(GENERATOR)"=="ninja"', {
+                'write_only_new': '1',
+              }, {
+                'write_only_new': '0',
+              }],
+            ],
           },
           'inputs': [
             '<(grit_grd_file)',
             '<!@pymod_do_main(grit_info --inputs)',
           ],
           'outputs': [
             '<(grit_out_dir)/grit/devtools_resources.h',
             '<(grit_out_dir)/devtools_resources.pak',
             '<(grit_out_dir)/grit/devtools_resources_map.cc',
             '<(grit_out_dir)/grit/devtools_resources_map.h',
           ],
           'action': ['<@(grit_cmd)',
                      '-i', '<(grit_grd_file)', 'build',
                      '-f', '<(DEPTH)/tools/gritsettings/resource_ids',
                      '-o', '<(grit_out_dir)',
+                     '--write-only-new=<(write_only_new)',
                      '-D', 'SHARED_INTERMEDIATE_DIR=<(SHARED_INTERMEDIATE_DIR)',
                      '<@(grit_defines)',
                      '<@(grit_rc_header_format)'],
           'message': 'Generating resources from <(grit_grd_file)',
         },
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '<(SHARED_INTERMEDIATE_DIR)',
         ]
       },
       'includes': [ '../../../build/grit_target.gypi' ],
     },
   ],
 }