Avoid argument name collision in DecodeLazyPixelRefEvent trace event

It is enough to pass LazyPixelRef argument only in TRACE_EVENT_BEGIN1.

BUG=None
R=caseq@chromium.org, pfeldman@chromium.org

Review URL: https://codereview.chromium.org/299803002

git-svn-id: svn://svn.chromium.org/blink/trunk@174449 bbb929c8-8fbe-4397-9dbb-9b2b20218538