Update blurred rrect mask filter creation method to also handle caching
Update blurred rrect mask filter creation method to also handle caching

The caching of the mask will also be required for the vertex attribute path so I moved that into the helper. The parameters computed by ComputeBlurredRRectParams will be needed to construct the coverage geometry by the vertex attribute path so I moved that out of the helper.

This is split out of https://codereview.chromium.org/2245653002/ (Start using vertex attributes for nine-patch blurred rrect draws)

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2249463002

Review-Url: https://codereview.chromium.org/2249463002

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