Issue acquire barrier in SkRefCnt::unique().
Issue acquire barrier in SkRefCnt::unique().

When unique() returns true, it must also issue an acquire barrier.
Note that this change may adversly impact SkPath performance,
but editing SkPaths is already a performance issue.

BUG=chromium:258499

No API changes.
TBR=reed@google.com

Review URL: https://codereview.chromium.org/687293002

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