GN: toolchain threading cleanup

tools/gn/ninja_toolchain_writer.cc

Index: tools/gn/ninja_toolchain_writer.cc
diff --git a/tools/gn/ninja_toolchain_writer.cc b/tools/gn/ninja_toolchain_writer.cc
index 310caba6f6bfa3f1f621462b53a4d74b19cdfdea..5f33e69810c6b626a1fc317e46257a0b594a9473 100644
--- a/tools/gn/ninja_toolchain_writer.cc
+++ b/tools/gn/ninja_toolchain_writer.cc
@@ -13,6 +13,7 @@
 #include "tools/gn/settings.h"
 #include "tools/gn/target.h"
 #include "tools/gn/toolchain.h"
+#include "tools/gn/toolchain_manager.h"
 #include "tools/gn/trace.h"
 
 NinjaToolchainWriter::NinjaToolchainWriter(
@@ -62,11 +63,14 @@ bool NinjaToolchainWriter::RunAndWriteFile(
 }
 
 void NinjaToolchainWriter::WriteRules() {
-  const Toolchain* tc = settings_->toolchain();
+  const Toolchain* tc = settings_->build_settings()->toolchain_manager()
+      .GetToolchainDefinitionUnlocked(settings_->toolchain_label());
+  CHECK(tc);
+
   std::string indent("  ");
 
   NinjaHelper helper(settings_->build_settings());
-  std::string rule_prefix = helper.GetRulePrefix(tc);
+  std::string rule_prefix = helper.GetRulePrefix(settings_);
 
   for (int i = Toolchain::TYPE_NONE + 1; i < Toolchain::TYPE_NUMTYPES; i++) {
     Toolchain::ToolType tool_type = static_cast<Toolchain::ToolType>(i);