Allow index sources to be unpremul.
Allow index sources to be unpremul.

This only affects the PNG image decoder, where we have already created
the color table without premultiplication. Since the RowProcChooser is
just providing a proc that chooses indices into the color table, it can
just return the same RowProc.

Update test_row_proc_choice. It was testing to ensure that we hadn't
changed the behavior from the original version of setPrefConfigTable.
In this case, we deliberately changed the behavior, so we need to
change the test.

BUG=b/12024301

Review URL: https://codereview.chromium.org/657863005

VRToxin-AOSP/android_external_skia,todotodoo/skia,samuelig/skia,Infinitive-OS/platform_external_skia,shahrzadmn/skia,boulzordev/android_external_skia,OneRom/external_skia,nvoron23/skia,boulzordev/android_external_skia,boulzordev/android_external_skia,PAC-ROM/android_external_skia,geekboxzone/mmallow_external_skia,vanish87/skia,qrealka/skia-hc,todotodoo/skia,rubenvb/skia,Igalia/skia,rubenvb/skia,spezi77/android_external_skia,todotodoo/skia,HalCanary/skia-hc,PAC-ROM/android_external_skia,pcwalton/skia,AOSP-YU/platform_external_skia,samuelig/skia,AOSP-YU/platform_external_skia,DiamondLovesYou/skia-sys,DiamondLovesYou/skia-sys,invisiblek/android_external_skia,aosp-mirror/platform_external_skia,chenlian2015/skia_from_google,AOSPB/external_skia,Infinitive-OS/platform_external_skia,VRToxin-AOSP/android_external_skia,qrealka/skia-hc,AOSPB/external_skia,AOSPB/external_skia,ominux/skia,scroggo/skia,todotodoo/skia,VRToxin-AOSP/android_external_skia,chenlian2015/skia_from_google,todotodoo/skia,jtg-gg/skia,timduru/platform-external-skia,w3nd1go/android_external_skia,Igalia/skia,HalCanary/skia-hc,pcwalton/skia,Hikari-no-Tenshi/android_external_skia,pcwalton/skia,PAC-ROM/android_external_skia,HalCanary/skia-hc,w3nd1go/android_external_skia,spezi77/android_external_skia,amyvmiwei/skia,PAC-ROM/android_external_skia,timduru/platform-external-skia,HalCanary/skia-hc,geekboxzone/mmallow_external_skia,spezi77/android_external_skia,google/skia,HalCanary/skia-hc,VRToxin-AOSP/android_external_skia,Igalia/skia,Jichao/skia,MarshedOut/android_external_skia,Igalia/skia,tmpvar/skia.cc,nfxosp/platform_external_skia,nfxosp/platform_external_skia,geekboxzone/mmallow_external_skia,TeamExodus/external_skia,invisiblek/android_external_skia,ominux/skia,aosp-mirror/platform_external_skia,TeamTwisted/external_skia,VRToxin-AOSP/android_external_skia,invisiblek/android_external_skia,MarshedOut/android_external_skia,Hikari-no-Tenshi/android_external_skia,shahrzadmn/skia,OneRom/external_skia,invisiblek/android_external_skia,TeamExodus/external_skia,rubenvb/skia,invisiblek/android_external_skia,Jichao/skia,shahrzadmn/skia,noselhq/skia,TeamTwisted/external_skia,MonkeyZZZZ/platform_external_skia,HalCanary/skia-hc,ominux/skia,rubenvb/skia,VRToxin-AOSP/android_external_skia,qrealka/skia-hc,MarshedOut/android_external_skia,TeamExodus/external_skia,samuelig/skia,samuelig/skia,MarshedOut/android_external_skia,TeamTwisted/external_skia,nvoron23/skia,geekboxzone/mmallow_external_skia,nfxosp/platform_external_skia,nvoron23/skia,pcwalton/skia,Hikari-no-Tenshi/android_external_skia,geekboxzone/mmallow_external_skia,noselhq/skia,rubenvb/skia,AOSPB/external_skia,noselhq/skia,Igalia/skia,vanish87/skia,nvoron23/skia,TeamTwisted/external_skia,vanish87/skia,TeamExodus/external_skia,vanish87/skia,MonkeyZZZZ/platform_external_skia,google/skia,UBERMALLOW/external_skia,BrokenROM/external_skia,google/skia,Jichao/skia,ominux/skia,TeamExodus/external_skia,jtg-gg/skia,w3nd1go/android_external_skia,Infinitive-OS/platform_external_skia,noselhq/skia,rubenvb/skia,nvoron23/skia,ominux/skia,jtg-gg/skia,vanish87/skia,TeamExodus/external_skia,spezi77/android_external_skia,qrealka/skia-hc,BrokenROM/external_skia,DiamondLovesYou/skia-sys,google/skia,tmpvar/skia.cc,shahrzadmn/skia,VRToxin-AOSP/android_external_skia,aosp-mirror/platform_external_skia,chenlian2015/skia_from_google,AOSP-YU/platform_external_skia,AOSPB/external_skia,ominux/skia,jtg-gg/skia,OneRom/external_skia,AOSP-YU/platform_external_skia,Hikari-no-Tenshi/android_external_skia,amyvmiwei/skia,qrealka/skia-hc,AOSP-YU/platform_external_skia,YUPlayGodDev/platform_external_skia,DiamondLovesYou/skia-sys,w3nd1go/android_external_skia,nvoron23/skia,Infinitive-OS/platform_external_skia,TeamTwisted/external_skia,google/skia,DiamondLovesYou/skia-sys,TeamTwisted/external_skia,jtg-gg/skia,nvoron23/skia,MinimalOS-AOSP/platform_external_skia,OneRom/external_skia,rubenvb/skia,MonkeyZZZZ/platform_external_skia,samuelig/skia,BrokenROM/external_skia,google/skia,Igalia/skia,w3nd1go/android_external_skia,AOSPB/external_skia,tmpvar/skia.cc,OneRom/external_skia,VRToxin-AOSP/android_external_skia,nvoron23/skia,todotodoo/skia,google/skia,shahrzadmn/skia,spezi77/android_external_skia,PAC-ROM/android_external_skia,nfxosp/platform_external_skia,BrokenROM/external_skia,HalCanary/skia-hc,invisiblek/android_external_skia,AOSP-YU/platform_external_skia,OneRom/external_skia,samuelig/skia,MinimalOS-AOSP/platform_external_skia,TeamTwisted/external_skia,pcwalton/skia,rubenvb/skia,geekboxzone/mmallow_external_skia,boulzordev/android_external_skia,MarshedOut/android_external_skia,PAC-ROM/android_external_skia,shahrzadmn/skia,TeamExodus/external_skia,amyvmiwei/skia,PAC-ROM/android_external_skia,HalCanary/skia-hc,timduru/platform-external-skia,DiamondLovesYou/skia-sys,pcwalton/skia,w3nd1go/android_external_skia,AOSPB/external_skia,shahrzadmn/skia,google/skia,amyvmiwei/skia,vanish87/skia,BrokenROM/external_skia,AOSP-YU/platform_external_skia,Jichao/skia,scroggo/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