Add BUILD.gn to build ui strings from grit.

Add BUILD.gn to build ui strings from grit.

In Debug configuration:

$ gn gen out/Debug_gn
$ ninja -C out/Debug_gn strings

In Release configuration:

$ gn gen out/Release_gn --args=is_debug=false
$ ninja -C out/Release_gn strings

BUG=None
TEST=see above
R=brettw@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266268

[tfarina, 2014-04-22 03:40:57]

Brett, I ran into this:

$ ninja -C out/Release_gn strings
ninja: Entering directory `out/Release_gn'
ninja: error: '../../ui/ui/tools/gritsettings/resource_ids', needed by
'gen/ui/base/strings/grit/ui_strings.h', missing and no known rule to make it

Looks like the path to resource_ids is not correct?

The code in the grit templace (grit_rule.gni) os:
resource_ids =                                                                 
   rebase_path("//tools/gritsettings/resource_ids", root_build_dir) 

Also, GYP gives me a way to specify the output of grit file through grit_out_dir
variable. Is it possible to do the same in GN?

In GYP the path looks like this:
out/Debug/gen/ui/ui_strings/grit/ui_strings.h

[tfarina, 2014-04-22 21:28:42]

Brett, ping?

[brettw, 2014-04-22 21:47:18]

lgtm

[tfarina, 2014-04-22 21:49:46]

Brett, no, not yet. Did you see my question? This does not work as is yet.

[tfarina, 2014-04-25 13:57:26]

For posterity: Brett sent me the fix for the grit template, which fixed the
problem I was seeing and said to apply it to this patch and go with the current
approval.

Thanks for fixing it Brett.

I'm going to run the trybots and if they look good, I will commit this.

[tfarina, 2014-04-25 23:01:47]

Committed patchset #3 manually as r266268 (presubmit successful).