Verify that the custom properties on a WebGL rendering context object are retained across GCs.

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".

PASS context.customProperty is "value"
PASS extensionObject.customProperty is "value"
PASS context.customProperty is "value"
PASS extensionObject.customProperty is "value"
PASS successfullyParsed is true

TEST COMPLETE