Support explicit pools in actions

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 a48a8b9f84679448814b0d06e8c65b3855fe7c08..911a4741ae705e8126d09989910f3ecb5d708596 100644
--- a/tools/gn/ninja_toolchain_writer.cc
+++ b/tools/gn/ninja_toolchain_writer.cc
@@ -46,6 +46,8 @@ void NinjaToolchainWriter::Run(
   for (int i = Toolchain::TYPE_NONE + 1; i < Toolchain::TYPE_NUMTYPES; i++) {
     Toolchain::ToolType tool_type = static_cast<Toolchain::ToolType>(i);
     const Tool* tool = toolchain_->GetTool(tool_type);
+    if (tool_type == Toolchain::TYPE_ACTION)
+      continue;
     if (tool)
       WriteToolRule(tool_type, tool, rule_prefix);
   }