Re: Align metronome mark at time signature or first musical element. Fixes #684. (issue1579041)

[hanwenn]

http://codereview.appspot.com/1579041/diff/42001/43004
File lily/metronome-engraver.cc (right):

http://codereview.appspot.com/1579041/diff/42001/43004#newcode109
lily/metronome-engraver.cc:109: }
this is out of style with the rest of lilypond code base.

The normal pattern is to use XXx_interface::has_interface (for
hard-coded interfaces), or grob->[internal_]has_interface(), to check
for softcoded interfaces.

The reason for this is that Grob names are only used as keys at creation
time, and for providing context in debugging (grep for ->name() ).

The rest of the code uses interface names rather grob name, so we can
easily swap in and out implementations of formatting behavior.

Sorry for coming with this after the fact, but could you fix the
implementation to be in accordance with this?  This engraver should call
grob->has_interface() for each of the symbols from
non-break-align-symbols.

thanks

http://codereview.appspot.com/1579041/