Revise use_system_harfbuzz logic

Revise use_system_harfbuzz logic

Why: running pkg-config during declare_args is nasty (since it always
runs, regardless of arg overrides).  Also, we don't have chrome_os or
official builds, and we can just declare to use it for is_linux but not
fnl.

BUG=
R=jamesr@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/5c647eba3d25d5e78e6d2e46c26390f6ee0f597d

[lanechr, 2015-10-20 23:56:07]

lanechr@google.com changed reviewers:
+ cstout@google.com, jamesr@chromium.org

[jamesr, 2015-10-21 00:25:47]

lgtm

https://codereview.chromium.org/1409033003/diff/1/third_party/harfbuzz-ng/BUI...
File third_party/harfbuzz-ng/BUILD.gn (right):

https://codereview.chromium.org/1409033003/diff/1/third_party/harfbuzz-ng/BUI...
third_party/harfbuzz-ng/BUILD.gn:16: use_system_harfbuzz = is_linux && target_os
!= "fnl"
we should make an is_fnl as well (the is_linux, etc, things are the same as
target_os = checks but faster since they are bool checks instead of string
compares)

[cdotstout, 2015-10-21 00:35:53]

cstout@chromium.org changed reviewers:
+ cstout@chromium.org

[cdotstout, 2015-10-21 00:35:53]

https://codereview.chromium.org/1409033003/diff/1/third_party/harfbuzz-ng/BUI...
File third_party/harfbuzz-ng/BUILD.gn (right):

https://codereview.chromium.org/1409033003/diff/1/third_party/harfbuzz-ng/BUI...
third_party/harfbuzz-ng/BUILD.gn:16: use_system_harfbuzz = is_linux && target_os
!= "fnl"
On 2015/10/21 00:25:47, jamesr wrote:
> we should make an is_fnl as well (the is_linux, etc, things are the same as
> target_os = checks but faster since they are bool checks instead of string
> compares)

There already is.

[lanechr, 2015-10-21 00:37:47]

On 2015/10/21 00:35:53, cdotstout wrote:
>
https://codereview.chromium.org/1409033003/diff/1/third_party/harfbuzz-ng/BUI...
> File third_party/harfbuzz-ng/BUILD.gn (right):
> 
>
https://codereview.chromium.org/1409033003/diff/1/third_party/harfbuzz-ng/BUI...
> third_party/harfbuzz-ng/BUILD.gn:16: use_system_harfbuzz = is_linux &&
target_os
> != "fnl"
> On 2015/10/21 00:25:47, jamesr wrote:
> > we should make an is_fnl as well (the is_linux, etc, things are the same as
> > target_os = checks but faster since they are bool checks instead of string
> > compares)
> 
> There already is.

Switched to is_fnl

[lanechr, 2015-10-21 18:50:17]

Committed patchset #2 (id:20001) manually as
5c647eba3d25d5e78e6d2e46c26390f6ee0f597d (presubmit successful).