Fix the broken build.

1. When protocol buffers support is enabled CompressedRowSparseMatrix
   has a missing virtual method.
2. When SuiteSparse is missing, covariance_test tries to run the
   large scale covariance computation test.

Thanks to Alex Stewart for reporting #1.

Change-Id: I4238c966036362175e31749595ea8bb6f12a696c

internal/ceres/compressed_row_sparse_matrix.h

diff --git a/internal/ceres/compressed_row_sparse_matrix.h b/internal/ceres/compressed_row_sparse_matrix.h
index d65d5c7..d60b580 100644
--- a/internal/ceres/compressed_row_sparse_matrix.h
+++ b/internal/ceres/compressed_row_sparse_matrix.h
@@ -36,6 +36,7 @@
 #include "ceres/internal/port.h"
 #include "ceres/sparse_matrix.h"
 #include "ceres/types.h"
+#include "glog/logging.h"
 
 namespace ceres {
 
@@ -91,6 +92,13 @@
   virtual const double* values() const { return &values_[0]; }
   virtual double* mutable_values() { return &values_[0]; }
 
+#ifndef CERES_NO_PROTOCOL_BUFFERS
+  // Dump the sparse matrix to a proto. Destroys the contents of proto.
+  virtual void ToProto(SparseMatrixProto* proto) const {
+    LOG(FATAL) << "Broken.;";
+  }
+#endif
+
   // Delete the bottom delta_rows.
   // num_rows -= delta_rows
   void DeleteRows(int delta_rows);

internal/ceres/covariance_test.cc

diff --git a/internal/ceres/covariance_test.cc b/internal/ceres/covariance_test.cc
index bd0a0e2..f9c5cd4 100644
--- a/internal/ceres/covariance_test.cc
+++ b/internal/ceres/covariance_test.cc
@@ -398,8 +398,11 @@
   };
 
   Covariance::Options options;
+
+#ifndef CERES_NO_SUITESPARSE
   options.use_dense_linear_algebra = false;
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
+#endif
 
   options.use_dense_linear_algebra = true;
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
@@ -441,8 +444,10 @@
   Covariance::Options options;
   options.num_threads = 4;
 
+#ifndef CERES_NO_SUITESPARSE
   options.use_dense_linear_algebra = false;
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
+#endif
 
   options.use_dense_linear_algebra = true;
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
@@ -484,8 +489,11 @@
   };
 
   Covariance::Options options;
+
+#ifndef CERES_NO_SUITESPARSE
   options.use_dense_linear_algebra = false;
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
+#endif
 
   options.use_dense_linear_algebra = true;
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
@@ -533,10 +541,12 @@
    -0.00122,  -0.00122,  -0.00149,  -0.00298,   0.00000,   0.03457
   };
 
-
   Covariance::Options options;
+
+#ifndef CERES_NO_SUITESPARSE
   options.use_dense_linear_algebra = false;
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
+#endif
 
   options.use_dense_linear_algebra = true;
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);