ninja: Put generated sources in front of regular sources.
ninja: Put generated sources in front of regular sources.

This matches the behavior of the xcode generator.  As sources are generated by
actions and rules which run before the regular compile phase of a target, this
is a bit more intuitive and so I changed the ninja generator instead of the
xcode generator.

BUG=chromium:280718
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/24167002
old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google