Clamp radius in blur filters to a sensible value.

[gw3583]

Fixes #3118.

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This change is 

[gw3583]

r? @jrmuizel or @kvark

Pending try:
https://treeherder.mozilla.org/#/jobs?repo=try&revision=91d21a5d5b9c1110eb8c58c6adcdd572e79b97f3

(vs. pending baseline try against current WR master):
https://treeherder.mozilla.org/#/jobs?repo=try&revision=12aaadb0247fda06bf372038395260978b0cb17e

[kvark]

Reviewed 7 of 7 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @gw3583)

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webrender_api/src/display_item.rs, line 620 at r1 (raw file):

    /// Ensure that the parameters for a filter operation
    /// are sensible.
    pub fn sanitize(self) -> FilterOp {

nit: it would look much simpler if it was &mut self

[gw3583]

Try looks good.

@bors-servo r=kvark

[bors-servo]

📌 Commit ebe50f2 has been approved by kvark

[bors-servo]

⌛ Testing commit ebe50f2 with merge 7d1f150...

[bors-servo]

☀️ Test successful - status-appveyor, status-taskcluster
Approved by: kvark
Pushing 7d1f150 to master...