Don't try to readback from the GPU for small blur sigmas
Don't try to readback from the GPU for small blur sigmas

This should revert Ganesh's small sigma handling behavior to back before:  https://skia-review.googlesource.com/c/skia/+/52400 (Reorganize blur filter to insert new implementation)

BUG=skia:7787
BUG=skia:7751
BUG=832838

Change-Id: I0ce6b888be534afb60336abf561e97741fa34684
Reviewed-on: https://skia-review.googlesource.com/121331
Commit-Queue: Robert Phillips <95e8ac5504948c7bf91b22c16a8dbb7ae7c66bfd@google.com>
Reviewed-by: Herb Derby <9e12a3d2bbf73546e47cc9958f6ba8f3215b7eaf@google.com>

Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,rubenvb/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,rubenvb/skia,rubenvb/skia,google/skia,HalCanary/skia-hc,rubenvb/skia,HalCanary/skia-hc,google/skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,google/skia,rubenvb/skia,google/skia,google/skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,google/skia,rubenvb/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,rubenvb/skia,google/skia,rubenvb/skia,aosp-mirror/platform_external_skia,rubenvb/skia,aosp-mirror/platform_external_skia,rubenvb/skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc