This change also adds two static libs, libbspatch and libbsdiff,
which encapsulate the dependencies of both the binaries and the
unit tests.

TEST=`mma external/bsdiff` and ran unittests on host and bullhead:NRC47C

Bug: 26971929
Change-Id: Ica0b17fa60f3ddf86d03ae12e6c099efbdd1296b

The source code has mixed style guides. The new introduced extents and
exfile modules had 4-spaces indents but one tab instead of two indents
probably due to bad editor cofiguration. These modules were first
introduced as local patches to the .ebuild file but later merged in the
git repository.

This patch fixes the style guide on all the files added by Chromium OS
(all the source files execpt bsdiff.c and bspatch.c). The remaining
file should be converted over to the Chromium style guide when parts
of it are modified. A .clang-format file is included in this patch to
help with that process.

Bug: None
Test: `make all test && ./unittests`; mm

Change-Id: Ief3c557cb35aae67871a5ccde8486af651b84a35

bsdiff and bspatch are in C and had no unittest. This patch keeps
those programs as C code, but adds the C++ gtest unittest framework
to allow testing them. Two simple unittests added to validate that the
unittests work.

BUG=None
TEST=make test; ./unittests

Change-Id: I8bca6b0c6bc5d5880464183d50a602c9886d20d0