GN: Replace mojo/system.gni with forwarding groups

GN: Replace mojo/system.gni with forwarding groups

Many targets in mojo need to depend on different targets depending on if
they are building in the static or component build. In gyp, this is done
with variables (since that's the only thing you have) and the GN build
initially copied these variables into //mojo/system.gni. This worked, but
is not very idomatic in GN. This replaces the variables with groups that
forward to the correct depenedency depending on the build type and
target type (encoded in the target name).

R=brettw@chromium.org, viettrungluu@chromium.org

Committed: https://crrev.com/bef0b9045da427c4f2212a5aeb0a878eddee0edc
Cr-Commit-Position: refs/heads/master@{#295137}

[jamesr, 2014-09-15 19:50:47]

jamesr@chromium.org changed reviewers:
+ acolwell@chromium.org

[jamesr, 2014-09-15 19:50:48]

acolwell@ - media/mojo/services/BUILD.gn
viettrungluu@ - mojo/
brettw@ - GN-foo

[acolwell GONE FROM CHROMIUM, 2014-09-15 20:31:25]

lgtm for media/mojo/services/BUILD.gn

[viettrungluu, 2014-09-15 21:47:50]

lgtm

[brettw, 2014-09-16 16:48:06]

concept lgtm, I didn't look at the code.

[jamesr, 2014-09-16 16:51:12]

The CQ bit was checked by jamesr@chromium.org

[commit-bot: I haz the power, 2014-09-16 16:51:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/554363005/1

[commit-bot: I haz the power, 2014-09-16 16:58:24]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-16 16:58:26]

Try jobs failed on following builders:
  android_arm64_dbg_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_arm64_d...)
  android_clang_dbg_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)

[jamesr, 2014-09-16 19:24:08]

The CQ bit was checked by jamesr@chromium.org

[commit-bot: I haz the power, 2014-09-16 19:24:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/554363005/20001

[commit-bot: I haz the power, 2014-09-16 20:23:51]

Committed patchset #2 (id:20001) as 4390ec9dc6f70908db2ac24b8827db3259f65bb1

[commit-bot: I haz the power, 2014-09-16 20:24:26]

Patchset 2 (id:??) landed as
https://crrev.com/bef0b9045da427c4f2212a5aeb0a878eddee0edc
Cr-Commit-Position: refs/heads/master@{#295137}