This is a meta bug about factoring a TestRunner.a out of DumpRenderTree that can be shared by DumpRenderTree and ContentShell.
I'm also posting this patch series on GitHub if you want to see how it all fits together:
At this point, the remaining work is to move the DRTTestRunner class into the TestRunner library.
DRTTestRunner is no more. The remaining issues are cleaning up the API and making the library a component