bug 1510447 - Fix a blob image key leak. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D13262

--HG--
extra : source : a58f38fb47f3f436584a816ccbbc192ae9684d02
extra : intermediate-source : 6cca1b66a9dd1951abd51f6c3bf588a2ae46934c

gfx/layers/wr/WebRenderUserData.cpp

@@ -306,6 +306,7 @@ WebRenderFallbackData::WebRenderFallbackData(WebRenderLayerManager* aWRManager,
 
 WebRenderFallbackData::~WebRenderFallbackData()
 {
+  ClearImageKey();
 }
 
 nsDisplayItemGeometry*