This makes doing an SDK build in the Fuchsia tree easier.
The previous attempt at this change failed in gyp builds targeting xcode.
They failed because input lists for actions of the same target (e.g. the
actions for dartanalyzer) are merged and de-duped when the lists contain
relative paths, but merged and *not* de-duped when the lists contain
absolute paths. gyp rejects xcode files that it generated itself
when they contain duplicate entries.
This CL works around that bug, by using absolute paths in the GN build
and keeping relative paths in the gyp build.
R=rmacnak@google.com
Review-Url: https://codereview.chromium.org/2567213002 .
asiva