Consolidate path handling for test data files.

Added CERES_TEST_SRCDIR_POSTFIX macro.
Added TestFileAbsolutePath function.

Change-Id: I223b74af027bfb775447e062edab897395b21514

internal/ceres/visibility_based_preconditioner_test.cc

diff --git a/internal/ceres/visibility_based_preconditioner_test.cc b/internal/ceres/visibility_based_preconditioner_test.cc
index 5c4a6e8..bf01acb 100644
--- a/internal/ceres/visibility_based_preconditioner_test.cc
+++ b/internal/ceres/visibility_based_preconditioner_test.cc
@@ -45,11 +45,10 @@
 #include "ceres/schur_eliminator.h"
 #include "ceres/stringprintf.h"
 #include "ceres/types.h"
+#include "ceres/test_util.h"
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-DECLARE_string(test_srcdir);
-
 namespace ceres {
 namespace internal {
 
@@ -65,9 +64,7 @@
 
  protected:
   void SetUp() {
-    string input_file =
-        JoinPath(FLAGS_test_srcdir,
-                       "problem-6-1384-000.lsqp"); // NOLINT
+    string input_file = TestFileAbsolutePath("problem-6-1384-000.lsqp");
 
     scoped_ptr<LinearLeastSquaresProblem> problem(
         CHECK_NOTNULL(CreateLinearLeastSquaresProblemFromFile(input_file)));