Fix FrontBufferedStreamTest

cherry-pick of b9e56c1ee6c4c8ae0a2e9247e504d92de4a6bfaa in master

Original message below:

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Fix FrontBufferedStreamTest

TBR=scroggo@google.com

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1747423002

Review URL: https://codereview.chromium.org/1747423002
NOTREECHECKS=true
NOTRY=true
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/1757703005
1 file changed