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