Fix bug in ico decodes
Fix bug in ico decodes

Some icos have been looking a bit strange in Gold.

Looks like the cause was that we were decoding to kUnpremul
accidentally.

BUG=skia:

Review URL: https://codereview.chromium.org/1321913003

rubenvb/skia,qrealka/skia-hc,tmpvar/skia.cc,google/skia,aosp-mirror/platform_external_skia,tmpvar/skia.cc,aosp-mirror/platform_external_skia,google/skia,rubenvb/skia,tmpvar/skia.cc,HalCanary/skia-hc,google/skia,rubenvb/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,qrealka/skia-hc,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,aosp-mirror/platform_external_skia,shahrzadmn/skia,Hikari-no-Tenshi/android_external_skia,shahrzadmn/skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,qrealka/skia-hc,shahrzadmn/skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,shahrzadmn/skia,rubenvb/skia,qrealka/skia-hc,google/skia,rubenvb/skia,rubenvb/skia,HalCanary/skia-hc,rubenvb/skia,aosp-mirror/platform_external_skia,tmpvar/skia.cc,shahrzadmn/skia,qrealka/skia-hc,aosp-mirror/platform_external_skia,qrealka/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,rubenvb/skia,tmpvar/skia.cc,aosp-mirror/platform_external_skia,rubenvb/skia,google/skia,shahrzadmn/skia,shahrzadmn/skia,qrealka/skia-hc,google/skia,HalCanary/skia-hc,tmpvar/skia.cc,tmpvar/skia.cc,tmpvar/skia.cc,google/skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,tmpvar/skia.cc,HalCanary/skia-hc,rubenvb/skia,shahrzadmn/skia,shahrzadmn/skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,qrealka/skia-hc,google/skia