Fix "libpng warning: iCCP: known incorrect sRGB profile"

Fix "libpng warning: iCCP: known incorrect sRGB profile"

There are 32 warnings emitted during the build process.
The cause of warning is that "libpng-1.6 is more stringent about checking
ICC profiles than previos versions"[1].

All png files in chromium-efl are converted by running following command:
$ find . -type f -name "*.png" -exec convert {} -strip {} \;

[1] http://stackoverflow.com/questions/22745076/libpng-warning-iccp-known-incorrect-srgb-profile

Bug: http://web.sec.samsung.net/bugzilla/show_bug.cgi?id=15534

Reviewed by: sns.park

Change-Id: Ic17441d15648d8fa776646e70d934b8bde0fd430
Signed-off-by: SeungSeop Park <sns.park@samsung.com>