Evaluate non-palette compression for palette image
Evaluate non-palette compression for palette image

Evaluate if for Palette images (num_colors <= 256), non-palette
compression path (Subtract green, predictor transform etc) yield an
optimal compression density.

This change reduces the WebP file (for palette images) size by 0.4% with
drop of 3-5% in compression speed.

Change-Id: I1ad66fa94db4fd7ba7bc215763791ef662cd4f42

kim42083/webm.libwebp,yohunl/libwebp,ericmckean/webm.libwebp,Maria1099/webm.libwebp,webmproject/libwebp,ttyangf/libwebp,webmproject/libwebp,PKRoma/libwebp,iniwf/webm.libwebp,ericmckean/webm.libwebp,webmproject/libwebp,kalli123/webm.libwebp,redengineer/libwebp,kleopatra999/webm.libwebp,reimaginemedia/webm.libwebp,ttyangf/libwebp,jiehu5114/libwebp,ericmckean/webm.libwebp,Acidburn0zzz/webm.libwebp,zofuthan/libwebp,Suvarna1488/webm.libwebp,Maria1099/webm.libwebp,comoyo/gonzo-libwebp,Maria1099/webm.libwebp,reimaginemedia/webm.libwebp,Maria1099/webm.libwebp,kalli123/webm.libwebp,altogother/webm.libwebp,jiehu5114/libwebp,Suvarna1488/webm.libwebp,rxl194/libwebp,altogother/webm.libwebp,rxl194/libwebp,kim42083/webm.libwebp,ya7lelkom/libwebp,kim42083/webm.libwebp,matanbs/webm.libwebp,redengineer/libwebp,Aexyn/libwebp,PKRoma/libwebp,jacklicn/libwebp,ttyangf/libwebp,webmproject/libwebp,abwiz0086/webm.libwebp,kleopatra999/webm.libwebp,rxl194/libwebp,jacklicn/libwebp,kalli123/webm.libwebp,iniwf/webm.libwebp,gshORTON/webm.libwebp,reimaginemedia/webm.libwebp,Maria1099/webm.libwebp,iniwf/webm.libwebp,ttyangf/libwebp,gshORTON/webm.libwebp,altogother/webm.libwebp,rxl194/libwebp,matanbs/webm.libwebp,redengineer/libwebp,jiehu5114/libwebp,Suvarna1488/webm.libwebp,PKRoma/libwebp,zofuthan/libwebp,matanbs/webm.libwebp,ya7lelkom/libwebp,jiehu5114/libwebp,Acidburn0zzz/webm.libwebp,kleopatra999/webm.libwebp,iniwf/webm.libwebp,Suvarna1488/webm.libwebp,yohunl/libwebp,abwiz0086/webm.libwebp,ttyangf/libwebp,imazen/libwebp,comoyo/gonzo-libwebp,kleopatra999/webm.libwebp,Acidburn0zzz/webm.libwebp,reimaginemedia/webm.libwebp,comoyo/gonzo-libwebp,yohunl/libwebp,Acidburn0zzz/webm.libwebp,imazen/libwebp,PKRoma/libwebp,kim42083/webm.libwebp,abwiz0086/webm.libwebp,abwiz0086/webm.libwebp,PKRoma/libwebp,Aexyn/libwebp,iniwf/webm.libwebp,matanbs/webm.libwebp,yohunl/libwebp,Aexyn/libwebp,Aexyn/libwebp,zofuthan/libwebp,ericmckean/webm.libwebp,abwiz0086/webm.libwebp,ya7lelkom/libwebp,Suvarna1488/webm.libwebp,jacklicn/libwebp,altogother/webm.libwebp,comoyo/gonzo-libwebp,gshORTON/webm.libwebp,matanbs/webm.libwebp,ya7lelkom/libwebp,gshORTON/webm.libwebp,imazen/libwebp,redengineer/libwebp,imazen/libwebp,imazen/libwebp,comoyo/gonzo-libwebp,jacklicn/libwebp,rxl194/libwebp,gshORTON/webm.libwebp,comoyo/gonzo-libwebp,redengineer/libwebp,kim42083/webm.libwebp,Acidburn0zzz/webm.libwebp,PKRoma/libwebp,kalli123/webm.libwebp,ya7lelkom/libwebp,zofuthan/libwebp,kleopatra999/webm.libwebp,yohunl/libwebp,Aexyn/libwebp,jacklicn/libwebp,comoyo/gonzo-libwebp,ericmckean/webm.libwebp,webmproject/libwebp,altogother/webm.libwebp,reimaginemedia/webm.libwebp,jiehu5114/libwebp,zofuthan/libwebp,kalli123/webm.libwebp