Remove SkMemoryStream::peek()
Remove SkMemoryStream::peek()

I'd like to add a new API to SkStream for peeking - i.e. reading some
bytes without advancing the stream. This will be implemented for the
streams where it makes sense. I think the function should look
something like the following:

size_t peek(void* buffer, size_t bytesToRead) {
     return this->onPeek(buffer, bytesToRead);
}

virtual size_t onPeek(void* buffer, size_t bytesToRead) {
    return 0;   // unimplemented base class.
}

In order to avoid confusion, I'd like to remove SkMemoryStream::peek(),
which is not currently used internally, by Chrome, or by Android as far
as I can tell. There is also another function does the same thing:
getPosition().

BUG=skia:3257

Review URL: https://codereview.chromium.org/1039373002

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