Put gn generator rule to console pool

This allows gn to emit colorful diagnostics while regenerating
from ninja

Change-Id: I1160234db161899c9c762ddca25b1c63f9baa95f
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/10421
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>

src/gn/ninja_build_writer.cc

diff --git a/src/gn/ninja_build_writer.cc b/src/gn/ninja_build_writer.cc
index f801fb6..164c1d5 100644
--- a/src/gn/ninja_build_writer.cc
+++ b/src/gn/ninja_build_writer.cc
@@ -281,6 +281,8 @@
        << build_settings_->ninja_required_version().Describe() << "\n\n";
   out_ << "rule gn\n";
   out_ << "  command = " << GetSelfInvocationCommand(build_settings_) << "\n";
+  // Putting gn rule to console pool for colorful output on regeneration
+  out_ << "  pool = console\n";
   out_ << "  description = Regenerating ninja files\n\n";
 
   // This rule will regenerate the ninja files when any input file has changed.