Fix UseCounter usage in WindowPerformance

GetFrame() can be nullptr, so we should call GetExecutionContext() so we
do the null check before calling GetDocument().

Bug: 966314
Change-Id: I09adb1fce626a5211ba23cf96d4cec9dd7b99fc5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627634
Auto-Submit: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662784}
1 file changed