Create module system for VisualBench

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
8 files changed