When summaries are built in fallback mode, the only information stored
in the package bundle is (a) which libraries appear in the bundle, and
(b) where the source files can be found on disk. This is enough
information so that DDC will still be able to tell how libraries are
grouped into build units, but otherwise summary functionality is
disabled.
This is intended to be availadle as a temporary workaround so that if
a bug is found in the summary infrastructure, it won't prevent DDC
compilation from working (it will just make it slower).
R=scheglov@google.com
Review URL: https://codereview.chromium.org/1826353002 .
Paul Berry
ea189bd6dc