A fractional blur radius results in the inflation of the shadow rect moving the relative center of the primitive shadow rect.

This results in the box shadow being stretched incorrectly when applied to the clip mask.

This is a partial fix for https://bugzilla.mozilla.org/show_bug.cgi?id=1411693

Backed out changeset 9a347a546d90 (Bug 1522351) for wrench bustage in reftests/boxshadow/no-stretch.png CLOSED TREE

https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception&selectedJob=223850961&revision=9a347a546d90d87842ca160c836f8d0305b14b99

https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception&selectedJob=223850961

https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=223850961&repo=autoland&lineNumber=2662

[task 2019-01-24T20:18:09.557Z] REFTEST reftests/boxshadow/overlap1.yaml == reftests/boxshadow/overlap1.png
[task 2019-01-24T20:18:10.097Z] REFTEST reftests/boxshadow/overlap2.yaml == reftests/boxshadow/overlap2.png
[task 2019-01-24T20:18:10.674Z] REFTEST reftests/boxshadow/no-stretch.yaml == reftests/boxshadow/no-stretch.png
[task 2019-01-24T20:18:10.790Z] REFTEST TEST-UNEXPECTED-FAIL | reftests/boxshadow/no-stretch.yaml == reftests/boxshadow/no-stretch.png | image comparison, max difference: 100, number of differing pixels: 1463

Updated the reference image and re-queued in lando.

https://hg.mozilla.org/mozilla-central/rev/ec5b5e910ce1