Remove Google Storage scheme prefix correctly from gs base name in webpages_playback
Remove Google Storage scheme prefix correctly from gs base name in webpages_playback

In python, str.lstrip([chars]) means "lstrip any of the chars from str",
not "remove prefix". Thus "gs://skia".lstrip("gs://") yields "kia".

Replace with custom function stripping the prefix from lstrip()ed gs
base name.

Review URL: https://codereview.chromium.org/780493002

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