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

(vendor repository for script)

Change-Id: I8c010ddb1e52497cbb4874e33143e184c517d3c3

Conflicts:
	envsetup.sh
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
Prebuilt chromium: update again script for lollipop

Change-Id: I4e34feb26c1b4bec10fb751a10dbc52579d7cd07
Remove nulls from the edify generator.

These would break the scripts. WTF are they doing here?

Change-Id: I0c52335a27f7ae974279fde1c2461b2dba24d263
makefile: Add changelog generator (1/2)

add "export CHANGELOG=true" in build.sh

Change-Id: Ibfddd3afc2a0d5e3d3b865572f65c0e7b314f6be