Fix a warning in PictureBenchmark.

Forgot to change from false to NULL. False does the right thing,
but gives a warning. Fix the warning.

Review URL: https://codereview.appspot.com/6570049

git-svn-id: http://skia.googlecode.com/svn/trunk@5666 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed