This makes `/_mozilla/mozilla/webgl/context_creation_error.html` pass,
for example.

```
./ mach test-wpt --product servodriver \
  --binary etc/run_in_headless_android_emulator.py \
  --binary-arg servo-x86 \
  --binary-arg target/i686-linux-android/release/servo.apk \
  /_mozilla/mozilla/webgl/context_creation_error.html
```