Compute & report timing information for line searches.

- We now compute & report the cumulative time spent performing the
  following tasks as part of a line search:
  - Evaluation of the univariate cost function value & gradient.
  - Minimization of the interpolating polynomial.
  - Total time spent performing line searches.
- This information is now reported for all minimizers, although only in
  the case of a constrained problem for the TR minimizer.
- Remove LineSearch::Function abstraction in place of using
  LineSearchFunction implementation directly, and remove virtual
  functions from LineSearchFunction.
-- LineSearch::Function added an unnecessary level of abstraction since
   the user always had to create a LineSearchFunction anyway to use a
   Ceres Evaluator, and it added an unncessary virtual function call.

Change-Id: Ia4e1921d78f351ae119875aa97a3ea5e8b5d9877
8 files changed