Bug 1518840 - P1: Remove rendering blurs into texture cache. r=gw,emilio
Bug 1518840 - P1: Remove rendering blurs into texture cache. r=gw,emilio

Caching text-shadows into texture cache was leading to rendering artifacts with
missing shadows.  Switch to using the picture path for all picture blurs and
rely upon picture caching to reduce repetitive work.

Differential Revision: https://phabricator.services.mozilla.com/D17329

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/48cff9538a5ef2a070b0e9e78b373ceb784aaeff

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender