Hook up link pools in GN.

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 ae2b6c974e5339832a81a77e543855c8254d5c3f..0e26db13afcb08ee61f84dd77c710f453fab759b 100644
--- a/tools/gn/ninja_toolchain_writer.cc
+++ b/tools/gn/ninja_toolchain_writer.cc
@@ -105,8 +105,11 @@ void NinjaToolchainWriter::WriteToolRule(const Toolchain::ToolType type,
     out_ << kIndent << "deps = msvc" << std::endl;
   }
 
-  if (!tool->pool().empty())
-    out_ << kIndent << "pool = " << tool->pool() << std::endl;
+  // The link pool applies to linker tools. Don't count TYPE_ALINK since
+  // static libraries are not generally intensive to write.
+  if (type == Toolchain::TYPE_SOLINK || type == Toolchain::TYPE_LINK)
+    out_ << kIndent << "pool = link_pool\n";
+
   if (tool->restat())
     out_ << kIndent << "restat = 1" << std::endl;
 }