WebP support
WebP support

Usage: crosswalk-app build debug ./ --android-webp="80 80 100"
First number, quality of jpeg file. (0 - 100).
Second number, quality of png file. (0 - 100).
Third number, quality of png file alpha data. (0 - 100).

BUG=XWALK-3829

shawngao5/crosswalk-app-tools,shawngao5/crosswalk-app-tools