Reland "Grit: Avoid rebuilding all pak files when ID ranges do not change"

This reverts commit 9e9a0e96.

Reason for reland: Closing file before moving it to appease windows

Change-Id: Iaa9b51861232c98ef4bf7210f868dbe20544c5c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2040950
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739122}

tools/grit/grit/tool/update_resource_ids/__init__.py

@@ -69,7 +69,9 @@ from __future__ import print_function
 import collections
 import getopt
 import os
+import shutil
 import sys
+import tempfile
 
 from grit.tool import interface
 from grit.tool.update_resource_ids import assigner, common, parser, reader
@@ -106,12 +108,20 @@ def _MultiReplace(data, repl):
   return ''.join(res)
 
 
-def _WriteFile(output, new_data):
-  if output:
-    with open(output, 'wt') as fh:
-      fh.write(new_data)
-  else:
+def _WriteFileIfChanged(output, new_data):
+  if not output:
     sys.stdout.write(new_data)
+    return
+
+  # Avoid touching outputs if file contents has not changed so that ninja
+  # does not rebuild dependent when not necessary.
+  if os.path.exists(output) and _ReadData(output)[0] == new_data:
+    return
+
+  # Write to a temporary file to ensure atomic changes.
+  with tempfile.NamedTemporaryFile('wt', delete=False) as f:
+    f.write(new_data)
+  shutil.move(f.name, output)
 
 
 class _Args:
@@ -288,8 +298,8 @@ Other options:
       header.append('# Edit %s instead.' % rel_input_dir)
       header.append('#' * 80)
       new_data = '\n'.join(header + ['']) + new_data
-    _WriteFile(args.output, new_data)
+    _WriteFileIfChanged(args.output, new_data)
 
     if args.depfile:
       deps_data = '{}: {}'.format(args.output, ' '.join(sorted(seen_files)))
-      _WriteFile(args.depfile, deps_data)
+      _WriteFileIfChanged(args.depfile, deps_data)