The newly created VisualLightweightBenchModule is just the old VisualBench.cpp, but gutted to only include timing code.
Future CLs will harden this abstraction, but for this CL the module owns a backpointer to VisualBench.cpp for a couple of calls.
BUG=skia:
Review URL: https://codereview.chromium.org/1304083007
