build: Add chromium prebuilt support to envsetup.sh && The core Makefile

This adds a chromium_prebuilt function to envsetup.sh that is invoked by lunch to check
whether the chromium prebuilts are up-to-date or not. If not, it will be built from source
and then the new source built version will be pulled during brunch/mka bacon to become the
new prebuilts for future builds.

This is all opt-in through the USE_PREBUILT_CHROMIUM flag. Without it being set to 1,
none of this would be ran, and regular operations will go on.

PS13:
-use export TARGET_DEVICE
-replace git -C with params compatible to old git versions

Conflicts:
	core/Makefile
	envsetup.sh

Change-Id: Ia040423e90abc2ef647717a41d9d972bd90ba780
(cherry picked from commit 552d536b2645c5b54fc49976105a51564fcff61b)
Prebuilt chromium: Run a check for target device directory

this should fix the issue that arises if device fails and device is built again, chromium will error out because it thinks the prebuilt files exist (which they are not, directories are just created).

Signed-off-by: Ayysir <ayysir@aospal.com>
Change-Id: I595cab268e66c738ccae9900150b36d7f9626a6e
(cherry picked from commit cabd388bc2e55c83fd4103d93ecf595adb54e479)
build: Fix PreBuilt Chromium refs

Change-Id: Icc553d5be1e71d8c754bc85b6906252e5690b508
(cherry picked from commit 18538dcae770f33f6a802cd17e238b7f030d69b3)
Update chromium_prebuilt.sh for 5.0

Change-Id: Idfd9b28f048447bf69b0f1c710b0ee354eff829a
(cherry picked from commit ae9233f184e941111356ca2af2b8a008bf5ca581)