build.cc: constify BuildStatus

Signed-off-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
diff --git a/src/build.cc b/src/build.cc
index 771ec85..75671a6 100644
--- a/src/build.cc
+++ b/src/build.cc
@@ -96,7 +96,7 @@
   total_edges_ = total;
 }
 
-void BuildStatus::BuildEdgeStarted(Edge* edge) {
+void BuildStatus::BuildEdgeStarted(const Edge* edge) {
   assert(running_edges_.find(edge) == running_edges_.end());
   int start_time = (int)(GetTimeMillis() - start_time_millis_);
   running_edges_.insert(make_pair(edge, start_time));
@@ -290,7 +290,7 @@
   return out;
 }
 
-void BuildStatus::PrintStatus(Edge* edge, EdgeStatus status) {
+void BuildStatus::PrintStatus(const Edge* edge, EdgeStatus status) {
   if (config_.verbosity == BuildConfig::QUIET)
     return;
 
diff --git a/src/build.h b/src/build.h
index f8d877b..97773c4 100644
--- a/src/build.h
+++ b/src/build.h
@@ -240,7 +240,7 @@
 struct BuildStatus {
   explicit BuildStatus(const BuildConfig& config);
   void PlanHasTotalEdges(int total);
-  void BuildEdgeStarted(Edge* edge);
+  void BuildEdgeStarted(const Edge* edge);
   void BuildEdgeFinished(Edge* edge, bool success, const string& output,
                          int* start_time, int* end_time);
   void BuildLoadDyndeps();
@@ -261,7 +261,7 @@
                               EdgeStatus status) const;
 
  private:
-  void PrintStatus(Edge* edge, EdgeStatus status);
+  void PrintStatus(const Edge* edge, EdgeStatus status);
 
   const BuildConfig& config_;