Properly substitute variables that reference paths outside SRCDIR.

Properly substitute variables that reference paths outside SRCDIR.

Apply the same kind of trick added in r58 and use a define's base name if it
refers to a location outside SRCDIR; so far, GritNode::AssignFirstIds() would
parse a file name differently than _ReadFirstIdsFromFile() even though they
refer to the same entry.

TEST=in Chromium, make BUILDTYPE=Release builddir_name=/outside/srcdir/out tracing_resources
R=joi@chromium.org

Landing for original author raphael.kubo.da.costa@intel.com,
https://codereview.chromium.org/69463002/

Committed: https://code.google.com/p/grit-i18n/source/detail?r=138

[Jói, 2013-11-12 13:48:34]

Hi Raphael,

FYI.

Cheers,
Jói

[Jói, 2013-11-12 13:48:59]

Committed patchset #1 manually as r138 (presubmit successful).