Install png optimization commands for optimization levels >= 1

Install png optimization commands for optimization levels >= 1

The script optimize-png-files.sh requires optipng, advdef, and pngout when
running at optimization levels 1 and 2, but checks for these tools only at
level 2. This CL changes optimize-png-files.sh to also check for the
required tools at level 1 optimization.

TEST=Uninstall optipng and run the script with -o1 parameter.
R=oshima@chromium.org
BUG=None

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=223387

[please use gerrit instead, 2013-09-14 11:16:53]

Mitsuru: PTAL.

[oshima, 2013-09-16 17:13:15]

lgtm

[commit-bot: I haz the power, 2013-09-16 17:14:30]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rouslan@chromium.org/23757043/1

[commit-bot: I haz the power, 2013-09-16 19:57:20]

Change committed as 223387