Fix some crashes in GN.

Fix some crashes in GN.

GN would read past the end of the file if the last line was a comment that didn't end in a newline.

It also would get confused if an end-of-file was reached after an assignment or a unary operator.

BUG=478169
Committed: https://crrev.com/693c60569dce46d5b1d5e2befcce95f9c8f171da
Cr-Commit-Position: refs/heads/master@{#342417}

[brettw, 2015-08-07 17:58:04]

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

[brettw, 2015-08-07 18:13:18]

The CQ bit was checked by brettw@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-07 18:14:43]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1275853006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1275853006/1

[commit-bot: I haz the power, 2015-08-07 18:29:34]

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

[commit-bot: I haz the power, 2015-08-07 18:29:35]

Dry run: This issue passed the CQ dry run.

[jam, 2015-08-07 19:48:43]

lgtm

[brettw, 2015-08-07 19:49:25]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-08-07 19:50:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1275853006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1275853006/1

[commit-bot: I haz the power, 2015-08-07 19:55:24]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-07 19:56:02]

Patchset 1 (id:??) landed as
https://crrev.com/693c60569dce46d5b1d5e2befcce95f9c8f171da
Cr-Commit-Position: refs/heads/master@{#342417}