Ignore implicit functions

[liamappelbe]

For example, fields of a class have implicit getters and setters that are auto-generated by the VM/frontend:

class SomeClass {
  SomeClass() : x = 123;

  // Creates an implicit getter and setter that should be ignored.
  int x;
}

These functions are excluded from the vm_service source report, so they will always appear as misses in the final coverage report. This is ok, because we can just ignore them in the function coverage report too, since they will never contain functionality that the user should care about testing.

Also add a proper function coverage test.

Fixes dart-lang/tools#501

[kevmoo]

It's tough to see what would be skipped here. Could you include an example?

[liamappelbe]

It's tough to see what would be skipped here. Could you include an example?

Added an example to the CL description

[coveralls]

Coverage increased (+0.01%) to 93.084% when pulling b3eba93 on ignore_implicit_funcs into 92c480b on master.