SkBlurImageFilter_opt.h: break conditions into separate loops.
SkBlurImageFilter_opt.h: break conditions into separate loops.

This gives ~15% improvement on blur_image on Linux Z620,
and should allow me to implement cropping without
incurring a perf hit.

BUG=skia:
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review URL: https://codereview.chromium.org/1426583004

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