Move console error detection in browser tests to higher level

Move console error detection in browser tests to higher level

This is because there are JavaScript-based browser tests that aren't
WebUI-specific.

Also, figure out a way to integrate with:
https://codereview.chromium.org/2013573007/#msg14

I proposed to mmenke@ that we change:

  void logging::SetLogMessageHandler(...handler..);

to

  scoped_ptr<ListenerHandle> logging::AddLogMessageListener(...listener...);

This would be a semantic change for some existing consumers, but they all
seem to only want to listen to the contents and not actually handle them.

This would also allow logging to remain unchanged and remove global
overriding, which may have unexpected side-effects.

BUG=615626

[Dan Beam, 2016-09-15 21:24:44]

Description was changed from

==========
Move console error detection in browser tests to higher level

This is because there are JavaScript-based browser tests that aren't
WebUI-specific.

Also, figure out a way to integrate with:
https://codereview.chromium.org/2013573007/#msg14

I proposed to mmenke@ that we change:

  void logging::SetLogMessageHandler(...handler..);

to

  scoped_ptr<ListenerHandle> logging::AddLogMessageListener(...listener...);

This would be a semantic change for some existing consumers, but they all
seem to only want to listen to the contents and not actually handle them.

This would also allow logging to remain unchanged and remove global
overriding, which may have unexpected side-effects.

BUG=615626
==========

to

==========
Move console error detection in browser tests to higher level

This is because there are JavaScript-based browser tests that aren't
WebUI-specific.

Also, figure out a way to integrate with:
https://codereview.chromium.org/2013573007/#msg14

I proposed to mmenke@ that we change:

  void logging::SetLogMessageHandler(...handler..);

to

  scoped_ptr<ListenerHandle> logging::AddLogMessageListener(...listener...);

This would be a semantic change for some existing consumers, but they all
seem to only want to listen to the contents and not actually handle them.

This would also allow logging to remain unchanged and remove global
overriding, which may have unexpected side-effects.

BUG=615626
==========