Make Problem movable.

Add a default move constructor and move assignment operator.

https://github.com/ceres-solver/ceres-solver/issues/528

Change-Id: I16ecf367a800fde564c29e2b824cd4fb44111366

include/ceres/problem.h

diff --git a/include/ceres/problem.h b/include/ceres/problem.h
index 278d80f..a4a6c8f 100644
--- a/include/ceres/problem.h
+++ b/include/ceres/problem.h
@@ -189,8 +189,11 @@
   // invocation Problem(Problem::Options()).
   Problem();
   explicit Problem(const Options& options);
+  Problem(Problem&&) = default;
+  Problem& operator=(Problem&&) = default;
+
   Problem(const Problem&) = delete;
-  void operator=(const Problem&) = delete;
+  Problem& operator=(const Problem&) = delete;
 
   ~Problem();
 

internal/ceres/problem_test.cc

diff --git a/internal/ceres/problem_test.cc b/internal/ceres/problem_test.cc
index 038600c..b779524 100644
--- a/internal/ceres/problem_test.cc
+++ b/internal/ceres/problem_test.cc
@@ -122,6 +122,24 @@
   }
 };
 
+
+TEST(Problem, MoveConstructor) {
+  Problem src;
+  double x;
+  src.AddParameterBlock(&x, 1);
+  Problem dst(std::move(src));
+  EXPECT_TRUE(dst.HasParameterBlock(&x));
+}
+
+TEST(Problem, MoveAssignment) {
+  Problem src;
+  double x;
+  src.AddParameterBlock(&x, 1);
+  Problem dst;
+  dst = std::move(src);
+  EXPECT_TRUE(dst.HasParameterBlock(&x));
+}
+
 TEST(Problem, AddResidualWithNullCostFunctionDies) {
   double x[3], y[4], z[5];