Fix compilation of GLTestContext_angle.cpp"

TBR=robertphillips@google.com

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1850783003
BUG=skia:

Review URL: https://codereview.chromium.org/1850783003 .
1 file changed