Add support for generating PkgInfo for application bundle on iOS.

build/config/ios/rules.gni

Index: build/config/ios/rules.gni
diff --git a/build/config/ios/rules.gni b/build/config/ios/rules.gni
index d6413633829f6fa4be14ab248815c75d75f5c1b7..e526dec17b90ffa70d43289800b70b40f2ee6918 100644
--- a/build/config/ios/rules.gni
+++ b/build/config/ios/rules.gni
@@ -420,6 +420,17 @@ template("ios_app_bundle") {
     _output_name = invoker.output_name
   }
 
+  # TODO(sdefresne): some target downstream manually pack an PkgInfo, so
+  # allow controlling the generation of the PkgInfo file via an undocumented
+  # parameter until they are fixed.
+  _write_pkg_info = false
+  if (defined(invoker.write_pkg_info)) {
+    _write_pkg_info = invoker.write_pkg_info
+  }
+
+  assert(_write_pkg_info || !_write_pkg_info,
+         "prevents 'Assignment had no effect.' errors")
+
   _arch_executable_source = _target_name + "_arch_executable_sources"
   _arch_executable_target = _target_name + "_arch_executable"
   _lipo_executable_target = _target_name + "_executable"
@@ -634,6 +645,35 @@ template("ios_app_bundle") {
       ]
     }
 
+    if (_write_pkg_info) {
+      _create_pkg_info = target_name + "_pkg_info"
+      action(_create_pkg_info) {
+        forward_variables_from(invoker, [ "testonly" ])
+        script = "//build/config/mac/write_pkg_info.py"
+        sources = get_target_outputs(":$_generate_info_plist")
+        outputs = [
+          "$target_gen_dir/$target_name",

[rohitrao (ping after 24h), 2016/12/09 12:14:42]

Why is the output of this step not a file named PkgInfo?

[sdefresne, 2016/12/09 13:50:19]

$target_gen_dir does not depends on the current target name (only on the path to
the BUILD.gn file containing the target). It means that if two separate target
in the same BUILD.gn file use the ios_app_bundle target, they will both try to
generate the same file named PkgInfo.

If I change the line to "$target_gen_dir/PkfInfo", I get the following error
while running "gn gen":

Two or more targets generate the same output:
  gen/base/PkgInfo

This is can often be fixed by changing one of the target names, or by 
setting an output_name on one of them.

Collisions:
  //base:base_i18n_perftests_pkg_info
  //base:base_perftests_pkg_info
  //base:base_unittests_pkg_info

Since the target _bundle_data_pkg_info rename the file to PkgInfo while copying
to the bundle, there is not really a need to name the file PkgInfo while
creating it. If you really care about that, I can change this to
"$target_gen_dir/$target_name/PkgInfo" though.

[rohitrao (ping after 24h), 2016/12/09 13:51:51]

Nope, it was just unexpected.  Perhaps summarize what you just wrote into a
short comment?

+        ]
+        args = [ "--plist" ] + rebase_path(sources, root_build_dir) +
+               [ "--output" ] + rebase_path(outputs, root_build_dir)
+        deps = [
+          ":$_generate_info_plist",
+        ]
+      }
+
+      _bundle_data_pkg_info = target_name + "_bundle_data_pkg_info"
+      bundle_data(_bundle_data_pkg_info) {
+        forward_variables_from(invoker, [ "testonly" ])
+        sources = get_target_outputs(":$_create_pkg_info")
+        outputs = [
+          "{{bundle_resources_dir}}/PkgInfo",
+        ]
+        public_deps = [
+          ":$_create_pkg_info",
+        ]
+      }
+    }
+
     create_signed_bundle(_target_name) {
       forward_variables_from(invoker,
                              [
@@ -661,6 +701,9 @@ template("ios_app_bundle") {
         bundle_deps = []
       }
       bundle_deps += [ ":$_bundle_data_info_plist" ]
+      if (_write_pkg_info) {
+        bundle_deps += [ ":$_bundle_data_pkg_info" ]
+      }
 
       if (use_ios_simulator) {
         if (!defined(data_deps)) {