Add build_chromium util and master script.

This CL adds a utility to create Chromium builds using a specified Chromium and Skia hash. If no hash is specified then Chromium's ToT and Skia's LKGR hashes are used.
The utility also has the ability to apply Chromium / Blink / Skia patches to the checkout. The resultant builds are then uploaded to Google Storage. Has the ability to create APK builds if Android target_platform is specified.

Also contains the following improvements:
* gs.go can now upload subdirectories.
* glog is now flushed from all scripts to make sure all pending log IO is cleared.

BUG=skia:3163

Review URL: https://codereview.chromium.org/822023002
First rough pass at a Markdown server.

BUG=skia:

Review URL: https://codereview.chromium.org/821773002