vendor/omni: Add chromium_prebuilt.sh

This script will pull the necessary libs from a complete build and generate proper
makefiles in order to support using a prebuilt Chromium. Files are placed in
prebuilts/chromium/-devicenamehere-, and are not tracked by git, so they are completely
out of the way.

PS3:
-replace git -C with params compatible to old git versions

Change-Id: I3141defcbd4108178881f7203f3105aecc27378b
(cherry picked from commit 2aea4c5e122a6a12a1049c1881f23903bd93c9d9)
(cherry picked from commit 4c86a55ccd2ac65a53611d8c80f8fcfc810b0cb6)
vendor/omni: Fix-ups for prebuilt Chromium

- Make copying far more reliable, even on non-clean builds
- Use $OUT in script in all cases, apparently get_build_var OUT_DIR isn't reliable.
envsetup.sh, please -_-

Change-Id: I27fa9bc7a043c32bcb29e7667e86b40226222a5a

Conflicts:
	config/common.mk

(cherry picked from commit 840b2c51c7dd4002237c0435c02e8631a67a2170)
(cherry picked from commit 6ea61a3aeb81f98567a6cc3a156761d9c2cc4bb8)
Prebuilt chromium: update script for lollipop

Change-Id: I3fbef0d23e76a6f5c25579d1ca9336bcfe19290d
(cherry picked from commit 0add28f60b138fe4b65326968769a5bafb53d1a7)
(cherry picked from commit 503be39376540aa510faf14d3eed201b609defbd)