Update timestmap of file only when content is changed

This can reduce build steps in incremental build.

Bug: 810298
Change-Id: I8ef6c3aa908f5d6e2e8c57edf8d29ed80a0d1993
Reviewed-on: https://chromium-review.googlesource.com/1126892Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573483}

content/public/android/generate_child_service.py

@@ -42,11 +42,12 @@ def DoMain(argv):
   number = int(number)
 
   path_template = "org/chromium/content/app/SandboxedProcessService{0}.java"
-  with zipfile.ZipFile(output, 'w', zipfile.ZIP_STORED) as srcjar:
-    for i in xrange(number):
-      build_utils.AddToZipHermetic(srcjar,
-              path_template.format(i),
-              data=GenerateService(i))
+  with build_utils.AtomicOutput(output) as f:
+    with zipfile.ZipFile(f, 'w', zipfile.ZIP_STORED) as srcjar:
+      for i in xrange(number):
+        build_utils.AddToZipHermetic(srcjar,
+                                     path_template.format(i),
+                                     data=GenerateService(i))
 
   if options.depfile:
     build_utils.WriteDepfile(options.depfile, output)