There are failures on both WebKit Mac10.11 (dbg) and WebKit Win7 (dbg):
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_tests&tests=canvas-lose-restore-googol-size.html

For both, the expected vs. actual diff looks like this:
@@ -11,13 +11,13 @@
 PASS ctx.isContextLost() is true
 PASS contextLostTest is true
 PASS ctx.isContextLost() is true
-PASS successfullyParsed is true
-
-TEST COMPLETE
 PASS Graphics context lost event dispatched.
 PASS contextLostTest is true
 PASS ctx.isContextLost() is true
 PASS Context restored event dispatched after context lost.
 PASS contextLostTest is false
 PASS ctx.isContextLost() is false
+PASS successfullyParsed is true
 
+TEST COMPLETE
+

The test doesn't set jsTestIsAsync, so the "TEST COMPLETE" is triggered by the DOMContentLoaded event.

The fix is probably to use jsTestIsAsync + finishJSTest(), or to rewrite as testharness.js.