By 'make coverage', lcov is used to generate test coverage report in
HTML format stored in coverage_rpt folder.
BUG=chrome-os-partner:19235
TEST=Generate a report.
BRANCH=None
Change-Id: I44142eaaeb897cf09179764781120370920144cd
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/58203