When SkFlags encounters an invalid flag, quit.
When SkFlags encounters an invalid flag, quit.

This way the user knows to change their command line.

Review URL: https://codereview.chromium.org/12881014

git-svn-id: e8541e15acce502a64c929015570ad1648e548cd@8275 2bbb7eff-a529-9590-31e7-b0007b416f81

Hankuo/color-emoji.skia,Hankuo/color-emoji.skia,MatChung/color-emoji.skia,Hankuo/color-emoji.skia,Frankie-666/color-emoji.skia,MatChung/color-emoji.skia,Frankie-666/color-emoji.skia,Frankie-666/color-emoji.skia,MatChung/color-emoji.skia,Hankuo/color-emoji.skia,hbwhlklive/color-emoji.skia,hbwhlklive/color-emoji.skia,hbwhlklive/color-emoji.skia,Frankie-666/color-emoji.skia,MatChung/color-emoji.skia,hbwhlklive/color-emoji.skia,Frankie-666/color-emoji.skia,MatChung/color-emoji.skia,MatChung/color-emoji.skia,hbwhlklive/color-emoji.skia,Hankuo/color-emoji.skia,hbwhlklive/color-emoji.skia,Hankuo/color-emoji.skia,Frankie-666/color-emoji.skia