Modify the gn version of 'mb analyze' to handle GN group targets as well.

Modify the gn version of 'mb analyze' to handle GN group targets as well.

Previously, if a group target like 'mandoline:all' was specified as
an additional_compile_target that we wanted to build, the gn implementation
of 'analyze' would not handle it correctly (it could only handle dependencies
on files that existed in the build directory, like executables).

This patch modifies the MB implementation to also handle label-like targets
(the ninja mandoline:all target is the equivalent of the GN //mandonline:all
target); we do this by calling 'gn refs' twice, once looking for a list
of output paths to match against the compile targets and once looking for
a list of phony labels to match against the compile targets.

We also will match against just the target_name, so 'chrome_shell_apk' will
also match "//chrome/android:chrome_shell_apk'. This may result in
too many targets being rebuilt, but we can adjust that if need be.

This is somewhat inefficient, but the alternatives would be to either
1) force the user to specify the stamp files for a group, which would be
   ugly, or
2) force the user to specify all the compile targets in terms of GN labels,
   which would be different from how the recipes work w/ GYP and possibly
   require us to map binary names to targets outside of GN, which would
   be a maintenance headache.

R=scottmg@chromium.org,brettw@chromium.org
BUG=487035
CQ_EXTRA_TRYBOTS=tryserver.chromium.mac:mac_chromium_gn_rel;tryserver.chromium.win:win8_chromium_gn_rel

Committed: https://crrev.com/067d014b8f1918db09939aa765bdfa7576ab3d50
Cr-Commit-Position: refs/heads/master@{#329964}

[Dirk Pranke, 2015-05-13 23:37:21]

This patch depends on https://codereview.chromium.org/1131623006/ .

[scottmg, 2015-05-13 23:59:38]

lgtm

[brettw, 2015-05-14 16:38:26]

whatevs lgtm

[Dirk Pranke, 2015-05-14 20:22:34]

The CQ bit was checked by dpranke@chromium.org

[Dirk Pranke, 2015-05-14 20:22:40]

The CQ bit was unchecked by dpranke@chromium.org

[Dirk Pranke, 2015-05-14 21:37:53]

The CQ bit was checked by dpranke@chromium.org

[Dirk Pranke, 2015-05-14 21:37:54]

The patchset sent to the CQ was uploaded after l-g-t-m from brettw@chromium.org,
scottmg@chromium.org
Link to the patchset: https://codereview.chromium.org/1135743005/#ps60001
(title: "add the input target, not the build target, to the list of matches")

[commit-bot: I haz the power, 2015-05-14 21:39:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1135743005/60001

[commit-bot: I haz the power, 2015-05-14 22:52:54]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-05-14 22:54:44]

Patchset 4 (id:??) landed as
https://crrev.com/067d014b8f1918db09939aa765bdfa7576ab3d50
Cr-Commit-Position: refs/heads/master@{#329964}