Bug 1518774 - Disable test_invalid_mime_type_blob.html on android. r=smaug

This test is extremely heavy and, often, on android, it timeouts.

Differential Revision: https://phabricator.services.mozilla.com/D19690

--HG--
extra : rebase_source : dc1649720f20af493341a1c5d7b5b23776997707

dom/canvas/test/mochitest.ini

@@ -299,3 +299,4 @@ subsuite = gpu
 tags = offscreencanvas
 skip-if = 1
 [test_invalid_mime_type_blob.html]
+skip-if = toolkit == 'android'