[gcc] Fix build failure caused by error: multi-line comment [-Werror=comment] in focus_traversal_un…

[gcc] Fix build failure caused by error: multi-line comment [-Werror=comment] in focus_traversal_unittest.cc

gcc toolchain throws a warning for using a trailing '\' in a comment which begins with '//'.

clang toolchain doesn't throw any warning for this hence its not captured by our bots.

Compiler option -Wno-comment appended after -Wall fixes the above issue but results in having inconsistent
comments.

The code snippet at [1] cleverly avoids these warnings as shown.

[1] https://code.google.com/p/chromium/codesearch#chromium/src/extensions/browser/content_hash_tree.h&l=23

R=mgiuca@chromium.org
TBR=sky@chromium.org

Committed: https://crrev.com/74335ef1219dd2178a5e754e4c4d2ea160eae3c9
Cr-Commit-Position: refs/heads/master@{#314745}

[vivekg, 2015-02-04 11:37:48]

vivekg@chromium.org changed reviewers:
+ vivekg@chromium.org

[vivekg, 2015-02-04 11:37:49]

PTAL, thanks.

[Matt Giuca, 2015-02-04 23:07:34]

Thanks for finding this. I didn't know that a \ at the end of a comment
continues the comment (but it still seems strange that GCC warns about it given
that there is a comment on the next line).

Thanks for the creative fix. LGTM.

[Matt Giuca, 2015-02-04 23:08:14]

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

[Matt Giuca, 2015-02-04 23:08:14]

+brettw for OWNERS.

[Matt Giuca, 2015-02-04 23:09:35]

mgiuca@chromium.org changed reviewers:
+ sky@chromium.org
- brettw@chromium.org

[Matt Giuca, 2015-02-04 23:09:35]

Oh sorry, I got confused about who reviewed the original patch. It was sky.

-brettw
+sky for owners.

[vivekg, 2015-02-05 00:17:15]

The CQ bit was checked by vivekg@chromium.org

[commit-bot: I haz the power, 2015-02-05 00:18:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/874663003/1

[vivekg, 2015-02-05 00:21:39]

The CQ bit was unchecked by vivekg@chromium.org

[vivekg, 2015-02-05 03:56:50]

The CQ bit was checked by vivekg@chromium.org

[commit-bot: I haz the power, 2015-02-05 03:57:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/874663003/1

[commit-bot: I haz the power, 2015-02-05 04:01:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-05 04:02:16]

Patchset 1 (id:??) landed as
https://crrev.com/74335ef1219dd2178a5e754e4c4d2ea160eae3c9
Cr-Commit-Position: refs/heads/master@{#314745}