Add a relative source path variable to our gyp build process. This path lets us locate the src folder with respect to the generated output folder, for the pregenerated projects. Change-Id: I5cf36f35f68638572bc1a8aec1f570edf76a1c74 Reviewed-on: https://chromium-review.googlesource.com/178521 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Commit-Queue: Shannon Woods <shannonwoods@chromium.org> Tested-by: Shannon Woods <shannonwoods@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>