Add Status::Refresh(int64_t cur_time_millis) method.

Add a method to the abstract Status interface to refresh
the status after some time has passed. Implement it properly
in StatusPrinter.

+ Fix a bug in FormatProgressMessage() which ignored the
  value pass as argument (time_millis), and was using
  a member value instead (time_millis_). In practice, they
  were the same, but this is no longer true after this
  change.

src/status.h

@@ -34,6 +34,13 @@ struct Status {
   virtual void BuildStarted() = 0;
   virtual void BuildFinished() = 0;
 
+  /// Refresh status display after some time has passed.  Useful
+  /// when printing the status on an interactive terminal. Does
+  /// nothing by default. \arg cur_time_millis is the current time
+  /// expressed in milliseconds, using the same epoch than the
+  /// one used in BuildEdgeStart() and BuildEdgeFinished().
+  virtual void Refresh(int64_t cur_time_millis) {}
+
   /// Set the Explanations instance to use to report explanations,
   /// argument can be nullptr if no explanations need to be printed
   /// (which is the default).

src/status_printer.cc

@@ -304,13 +304,13 @@ string StatusPrinter::FormatProgressStatus(const char* progress_status_format,
 
         // Overall finished edges per second.
       case 'o':
-        SnprintfRate(finished_edges_ / (time_millis_ / 1e3), buf, "%.1f");
+        SnprintfRate(finished_edges_ / (time_millis / 1e3), buf, "%.1f");
         out += buf;
         break;
 
         // Current rate, average over the last '-j' jobs.
       case 'c':
-        current_rate_.UpdateRate(finished_edges_, time_millis_);
+        current_rate_.UpdateRate(finished_edges_, time_millis);
         SnprintfRate(current_rate_.rate(), buf, "%.1f");
         out += buf;
         break;
@@ -336,15 +336,15 @@ string StatusPrinter::FormatProgressStatus(const char* progress_status_format,
       case 'E':  // ETA, seconds
       case 'W':  // ETA, human-readable
       {
-        double elapsed_sec = time_millis_ / 1e3;
+        double elapsed_sec = time_millis / 1e3;
         double eta_sec = -1;  // To be printed as "?".
         if (time_predicted_percentage_ != 0.0) {
-          // So, we know that we've spent time_millis_ wall clock,
+          // So, we know that we've spent time_millis wall clock,
           // and that is time_predicted_percentage_ percent.
           // How much time will we need to complete 100%?
-          double total_wall_time = time_millis_ / time_predicted_percentage_;
+          double total_wall_time = time_millis / time_predicted_percentage_;
           // Naturally, that gives us the time remaining.
-          eta_sec = (total_wall_time - time_millis_) / 1e3;
+          eta_sec = (total_wall_time - time_millis) / 1e3;
         }
 
         const bool print_with_hours =
@@ -428,17 +428,28 @@ void StatusPrinter::PrintStatus(const Edge* edge, int64_t time_millis) {
 
   bool force_full_command = config_.verbosity == BuildConfig::VERBOSE;
 
-  string to_print = edge->GetBinding("description");
-  if (to_print.empty() || force_full_command)
-    to_print = edge->GetBinding("command");
+  last_description_ = edge->GetBinding("description");
+  if (last_description_.empty() || force_full_command)
+    last_description_ = edge->GetBinding("command");
 
-  to_print = FormatProgressStatus(progress_status_format_, time_millis)
-      + to_print;
+  RefreshStatus(time_millis, force_full_command);
+}
 
+void StatusPrinter::RefreshStatus(int64_t cur_time_millis,
+                                  bool force_full_command) {
+  std::string to_print =
+      FormatProgressStatus(progress_status_format_, cur_time_millis) +
+      last_description_;
   printer_.Print(to_print,
                  force_full_command ? LinePrinter::FULL : LinePrinter::ELIDE);
 }
 
+void StatusPrinter::Refresh(int64_t cur_time_millis) {
+  if (printer_.is_smart_terminal()) {
+    RefreshStatus(cur_time_millis, false);
+  }
+}
+
 void StatusPrinter::Warning(const char* msg, ...) {
   va_list ap;
   va_start(ap, msg);

src/status_printer.h

@@ -36,6 +36,8 @@ struct StatusPrinter : Status {
   void BuildStarted() override;
   void BuildFinished() override;
 
+  void Refresh(int64_t cur_time_millis) override;
+
   void Info(const char* msg, ...) override;
   void Warning(const char* msg, ...) override;
   void Error(const char* msg, ...) override;
@@ -82,6 +84,8 @@ struct StatusPrinter : Status {
   /// For how many edges we don't know the previous run time?
   int eta_unpredictable_edges_remaining_ = 0;
 
+  void RefreshStatus(int64_t cur_time_millis, bool force_full_command);
+
   void RecalculateProgressPrediction();
 
   /// Prints progress output.
@@ -93,6 +97,9 @@ struct StatusPrinter : Status {
   /// The custom progress status format to use.
   const char* progress_status_format_;
 
+  /// Last command's description or command-line.
+  std::string last_description_;
+
   template <size_t S>
   void SnprintfRate(double rate, char (&buf)[S], const char* format) const {
     if (rate == -1)