Speedup AnalyzeAndInit for low effort compression.
Speedup AnalyzeAndInit for low effort compression.

AnalyzeSubtractGreen constitutes about 8-10% of the comression CPU cycles.
Statistically, subtract-green is proved to be useful for most of the
non-palette compression. So instead of evaluating the entropy (by calling
AnalyzeSubtractGreen) apply subtract-green transform for the low-effort
compression.

This changes speeds up the compression at m=0 by 8-10% (with very slight loss
of 0.07% in the compression density).

Change-Id: I9797dc39437ae089716acb14631bbc77d367acf4

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