Report timings with microsecond resolution

In case one has a small problem to solve, where
completion is reached within a few milliseconds,
then four decimal places are not enough to accurately
represent the timings of all the separate sub-steps.
Thus, we extend the reported timings to include
six decimal places.

Change-Id: Iaf88a94a1b8896ea7370c75b1de2f05d8671206e

internal/ceres/gradient_problem_solver.cc

diff --git a/internal/ceres/gradient_problem_solver.cc b/internal/ceres/gradient_problem_solver.cc
index 488bff5..4add01c 100644
--- a/internal/ceres/gradient_problem_solver.cc
+++ b/internal/ceres/gradient_problem_solver.cc
@@ -262,15 +262,15 @@
                 static_cast<int>(iterations.size()));
 
   StringAppendF(&report, "\nTime (in seconds):\n");
-  StringAppendF(&report, "\n  Cost evaluation     %23.4f (%d)\n",
+  StringAppendF(&report, "\n  Cost evaluation     %23.6f (%d)\n",
                 cost_evaluation_time_in_seconds,
                 num_cost_evaluations);
-  StringAppendF(&report, "  Gradient evaluation %23.4f (%d)\n",
+  StringAppendF(&report, "  Gradient evaluation %23.6f (%d)\n",
                 gradient_evaluation_time_in_seconds,
                 num_gradient_evaluations);
-  StringAppendF(&report, "  Polynomial minimization   %17.4f\n",
+  StringAppendF(&report, "  Polynomial minimization   %17.6f\n",
                 line_search_polynomial_minimization_time_in_seconds);
-  StringAppendF(&report, "Total               %25.4f\n\n",
+  StringAppendF(&report, "Total               %25.6f\n\n",
                 total_time_in_seconds);
 
   StringAppendF(&report, "Termination:        %25s (%s)\n",

internal/ceres/solver.cc

diff --git a/internal/ceres/solver.cc b/internal/ceres/solver.cc
index b4896c4..bee0e19 100644
--- a/internal/ceres/solver.cc
+++ b/internal/ceres/solver.cc
@@ -863,44 +863,44 @@
   }
 
   StringAppendF(&report, "\nTime (in seconds):\n");
-  StringAppendF(&report, "Preprocessor        %25.4f\n",
+  StringAppendF(&report, "Preprocessor        %25.6f\n",
                 preprocessor_time_in_seconds);
 
-  StringAppendF(&report, "\n  Residual evaluation %23.4f\n",
+  StringAppendF(&report, "\n  Residual evaluation %23.6f\n",
                 residual_evaluation_time_in_seconds);
   if (line_search_used) {
-    StringAppendF(&report, "    Line search cost evaluation    %10.4f\n",
+    StringAppendF(&report, "    Line search cost evaluation    %10.6f\n",
                   line_search_cost_evaluation_time_in_seconds);
   }
-  StringAppendF(&report, "  Jacobian evaluation %23.4f\n",
+  StringAppendF(&report, "  Jacobian evaluation %23.6f\n",
                 jacobian_evaluation_time_in_seconds);
   if (line_search_used) {
-    StringAppendF(&report, "    Line search gradient evaluation   %6.4f\n",
+    StringAppendF(&report, "    Line search gradient evaluation   %6.6f\n",
                   line_search_gradient_evaluation_time_in_seconds);
   }
 
   if (minimizer_type == TRUST_REGION) {
-    StringAppendF(&report, "  Linear solver       %23.4f\n",
+    StringAppendF(&report, "  Linear solver       %23.6f\n",
                   linear_solver_time_in_seconds);
   }
 
   if (inner_iterations_used) {
-    StringAppendF(&report, "  Inner iterations    %23.4f\n",
+    StringAppendF(&report, "  Inner iterations    %23.6f\n",
                   inner_iteration_time_in_seconds);
   }
 
   if (line_search_used) {
-    StringAppendF(&report, "  Line search polynomial minimization  %.4f\n",
+    StringAppendF(&report, "  Line search polynomial minimization  %.6f\n",
                   line_search_polynomial_minimization_time_in_seconds);
   }
 
-  StringAppendF(&report, "Minimizer           %25.4f\n\n",
+  StringAppendF(&report, "Minimizer           %25.6f\n\n",
                 minimizer_time_in_seconds);
 
-  StringAppendF(&report, "Postprocessor        %24.4f\n",
+  StringAppendF(&report, "Postprocessor        %24.6f\n",
                 postprocessor_time_in_seconds);
 
-  StringAppendF(&report, "Total               %25.4f\n\n",
+  StringAppendF(&report, "Total               %25.6f\n\n",
                 total_time_in_seconds);
 
   StringAppendF(&report, "Termination:        %25s (%s)\n",