Evaluate ResidualBlocks without LossFunction if needed.

1. Add the ability to evaluate the problem without loss function.
2. Remove static Evaluator::Evaluate
3. Refactor the common code from problem_test.cc and
   evaluator_test.cc into evaluator_test_utils.cc

Change-Id: I1aa841580afe91d288fbb65288b0ffdd1e43e827
diff --git a/internal/ceres/residual_block_utils_test.cc b/internal/ceres/residual_block_utils_test.cc
index 24723b3..d3c917a 100644
--- a/internal/ceres/residual_block_utils_test.cc
+++ b/internal/ceres/residual_block_utils_test.cc
@@ -62,7 +62,8 @@
   double jacobian;
   double* jacobians[] = { &jacobian };
 
-  EXPECT_EQ(residual_block.Evaluate(&cost,
+  EXPECT_EQ(residual_block.Evaluate(true,
+                                    &cost,
                                     &residuals,
                                     jacobians,
                                     scratch.get()), is_good);