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

For the file I'm testing with (c/b/resources/about_stats.html),
a rebuild runs 101 edges and compiles a bunch of cc files and takes 40s.
This reduces build times from 40s to 9.6s and reduces the number
of edges to 37.

BUG=439182
R=brettw@chromium.org

Review URL: https://codereview.chromium.org/740463005

Cr-Original-Commit-Position: refs/heads/master@{#306945}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 9261dde33f1939f432cafe6f9654efedba4dc252

grit_action.gypi

@@ -21,6 +21,20 @@
     # instead of build/common.gypi .
     'grit_additional_defines%': [],
     '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': [
     '<!@pymod_do_main(grit_info <@(grit_defines) <@(grit_additional_defines) '
@@ -35,6 +49,7 @@
              '-i', '<(grit_grd_file)', 'build',
              '-f', '<(grit_resource_ids)',
              '-o', '<(grit_out_dir)',
+             '--write-only-new=<(write_only_new)',
              '<@(grit_defines)',
              '<@(grit_additional_defines)',
              '<@(grit_rc_header_format)'],

secondary/tools/grit/grit_rule.gni

@@ -381,6 +381,7 @@ template("grit") {
               ".",
               "--depfile",
               rebase_path(depfile, root_build_dir),
+              "--write-only-new=1"
             ] + grit_defines
 
     # Add extra defines with -D flags.