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

content/browser/devtools/devtools_resources.gyp

Index: content/browser/devtools/devtools_resources.gyp
diff --git a/content/browser/devtools/devtools_resources.gyp b/content/browser/devtools/devtools_resources.gyp
index 3b82cc36a39920e6f33952557910cb7af9548a99..e246e2292930969c466a9aa5b425de5566732778 100644
--- a/content/browser/devtools/devtools_resources.gyp
+++ b/content/browser/devtools/devtools_resources.gyp
@@ -23,6 +23,21 @@
             '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)',
@@ -38,6 +53,7 @@
                      '-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)'],