Support explicit pools in actions

tools/gn/toolchain.h

Index: tools/gn/toolchain.h
diff --git a/tools/gn/toolchain.h b/tools/gn/toolchain.h
index 7b61f349b9c6065b9e9f0ecd7fb9316e0a127e37..368c2db4bfd3491ce8b85de6e89aac3194592da3 100644
--- a/tools/gn/toolchain.h
+++ b/tools/gn/toolchain.h
@@ -47,6 +47,7 @@ class Toolchain : public Item {
     TYPE_COPY,
     TYPE_COPY_BUNDLE_DATA,
     TYPE_COMPILE_XCASSETS,
+    TYPE_ACTION,
 
     TYPE_NUMTYPES  // Must be last.
   };
@@ -65,6 +66,7 @@ class Toolchain : public Item {
   static const char* kToolCopy;
   static const char* kToolCopyBundleData;
   static const char* kToolCompileXCAssets;
+  static const char* kToolAction;
 
   // The Settings of an Item is always the context in which the Item was
   // defined. For a toolchain this is confusing because this is NOT the