Roll GN (via buildtools) 321178:326666

Roll GN (via buildtools) 321178:326666

This picks up the changes for 'gn help all' and
the markdown docs, fixes a bug related to the
transitive propagation of public_deps across
shared objects, and includes a speculative fix
for the WriteFile() failures we're seeing on
Windows.

TBR=brettw@chromium.org

Committed: https://crrev.com/a21c4f2acc0b7b97a65c3c145361aed55c53f769
Cr-Commit-Position: refs/heads/master@{#326704}

[Dirk Pranke, 2015-04-23 23:16:48]

The CQ bit was checked by dpranke@chromium.org

[Dirk Pranke, 2015-04-23 23:17:01]

The CQ bit was unchecked by dpranke@chromium.org

[Dirk Pranke, 2015-04-23 23:17:55]

dpranke@chromium.org changed reviewers:
+ brettw@chromium.org

[Dirk Pranke, 2015-04-23 23:17:59]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2015-04-23 23:18:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1082813004/20001

[commit-bot: I haz the power, 2015-04-24 00:39:13]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-24 00:40:20]

Patchset 2 (id:??) landed as
https://crrev.com/a21c4f2acc0b7b97a65c3c145361aed55c53f769
Cr-Commit-Position: refs/heads/master@{#326704}

[horo, 2015-04-24 01:37:04]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/1095553006/ by horo@chromium.org.

The reason for reverting is: Caused gyp_flag_compare failure on Linux GN bots.

BUG=480739.