Optimize the ripple effect on the navigation bar in Files app.

Optimize the ripple effect on the navigation bar in Files app.

Due to slow querySelector (7ms) in the command handler, the ripple was far from
smooth. This CL replaces querySelector with getElementsByClassName which is
around 20 times faster.

TEST=Tested manually that the ripple is smooth.
BUG=455055
Committed: https://crrev.com/489a61ed8f0ed4538a856572ff9979a6f3e01b12
Cr-Commit-Position: refs/heads/master@{#314499}

[mtomasz, 2015-02-04 03:32:55]

mtomasz@chromium.org changed reviewers:
+ fukino@chromium.org

[mtomasz, 2015-02-04 03:33:02]

@fukino: PTAL. Thanks.

[fukino, 2015-02-04 03:34:47]

Wow! Thanks!!!
lgtm.

[mtomasz, 2015-02-04 03:40:34]

Thanks!

[mtomasz, 2015-02-04 03:40:37]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2015-02-04 03:40:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/895633005/1

[commit-bot: I haz the power, 2015-02-04 04:09:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-04 04:11:11]

Patchset 1 (id:??) landed as
https://crrev.com/489a61ed8f0ed4538a856572ff9979a6f3e01b12
Cr-Commit-Position: refs/heads/master@{#314499}