tools/gn: make use of base's StartsWith() function

tools/gn: make use of base's StartsWith() function

Since Brett introduced this funtion to base, we can make use of it and
remove our copy from gn. We are also making use of it in other five
files already.

BUG=None
TEST=gn gen + gn_unittests
R=scottmg@chromium.org

Committed: https://crrev.com/934d88d64c50f9f4d684194320cf15cd9b29059e
Cr-Commit-Position: refs/heads/master@{#362446}

[scottmg, 2015-12-01 16:42:06]

lgtm

[tfarina, 2015-12-01 17:33:42]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-12-01 17:34:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1481403006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1481403006/1

[commit-bot: I haz the power, 2015-12-01 17:41:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-12-01 17:42:58]

Description was changed from

==========
tools/gn: make use of base's StartsWith() function

Since Brett introduced this funtion to base, we can make use of it and
remove our copy from gn. We are also making use of it in other five
files already.

BUG=None
TEST=gn gen + gn_unittests
R=scottmg@chromium.org
==========

to

==========
tools/gn: make use of base's StartsWith() function

Since Brett introduced this funtion to base, we can make use of it and
remove our copy from gn. We are also making use of it in other five
files already.

BUG=None
TEST=gn gen + gn_unittests
R=scottmg@chromium.org

Committed: https://crrev.com/934d88d64c50f9f4d684194320cf15cd9b29059e
Cr-Commit-Position: refs/heads/master@{#362446}
==========

[commit-bot: I haz the power, 2015-12-01 17:42:58]

Patchset 1 (id:??) landed as
https://crrev.com/934d88d64c50f9f4d684194320cf15cd9b29059e
Cr-Commit-Position: refs/heads/master@{#362446}