Changed how tiles are copied to the master canvas.
Changed how tiles are copied to the master canvas.

This is in preparation for adding the powers of two mode.

Review URL: https://codereview.appspot.com/6464087

git-svn-id: e8541e15acce502a64c929015570ad1648e548cd@5254 2bbb7eff-a529-9590-31e7-b0007b416f81

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