Fix lint errors in evaluation_callback_test.cc

Change-Id: I63eb069544ad0d8f495490fe4caa07b9f04f7ec2

internal/ceres/evaluation_callback_test.cc

diff --git a/internal/ceres/evaluation_callback_test.cc b/internal/ceres/evaluation_callback_test.cc
index c8f257f..ccca942 100644
--- a/internal/ceres/evaluation_callback_test.cc
+++ b/internal/ceres/evaluation_callback_test.cc
@@ -260,19 +260,19 @@
   double counter_ = -1;
 };
 
-
 // r = IncrementingEvaluationCallback::counter - x
 struct EvaluationCallbackResidual {
-  EvaluationCallbackResidual(const IncrementingEvaluationCallback& callback)
-      : callback_(callback) {}
+  explicit EvaluationCallbackResidual(
+      const IncrementingEvaluationCallback& callback)
+      : callback(callback) {}
 
   template <typename T>
   bool operator()(const T* x, T* residuals) const {
-    residuals[0] = callback_.counter() - x[0];
+    residuals[0] = callback.counter() - x[0];
     return true;
   }
 
-  const IncrementingEvaluationCallback& callback_;
+  const IncrementingEvaluationCallback& callback;
 
   static CostFunction* Create(IncrementingEvaluationCallback& callback) {
     return new AutoDiffCostFunction<EvaluationCallbackResidual, 1, 1>(
@@ -298,9 +298,7 @@
   Problem problem(problem_options);
   problem.AddResidualBlock(LinearResidual::Create(), nullptr, &x);
   problem.AddResidualBlock(
-      EvaluationCallbackResidual::Create(*callback),
-      nullptr,
-      &y);
+      EvaluationCallbackResidual::Create(*callback), nullptr, &y);
   problem.SetParameterBlockConstant(&y);
 
   Solver::Options options;