Initialize Package earlier to evaluate commandline args earlier (fixes #1743)

On package initialization, flags from "chromium-args" are added to the Chromium commandline.
Previously, the Package object was initialized in the "PreMainMessageLoopRun" step.
As the GPU flags are already evaluated in the "BrowserThreadsStarted" step (which is before that), this was too late for flags like "--ignore-gpu-blacklist".