DM: add --multiPage option
DM: add --multiPage option

Motivation: I want to switch back to single-page output by default for
direct comparison to raster backends in Gold.

I can still test the multi-page option via a command-line switch.

BUG=skia:3721

Review URL: https://codereview.chromium.org/1063873004

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