Add support for user defined "pool" to GN.

tools/gn/tool.h

Index: tools/gn/tool.h
diff --git a/tools/gn/tool.h b/tools/gn/tool.h
index f6727ed6d16761ad58569e969def2ef92bcd4add..99b359460dd45862868322a385e1d9b62c064fda 100644
--- a/tools/gn/tool.h
+++ b/tools/gn/tool.h
@@ -9,9 +9,13 @@
 
 #include "base/logging.h"
 #include "base/macros.h"
+#include "tools/gn/label.h"
+#include "tools/gn/label_ptr.h"
 #include "tools/gn/substitution_list.h"
 #include "tools/gn/substitution_pattern.h"
 
+class Pool;
+
 class Tool {
  public:
   enum DepsFormat {
@@ -173,6 +177,11 @@ class Tool {
     rspfile_content_ = content;
   }
 
+  const LabelPtrPair<Pool> pool_label_pair() const { return pool_; }

[brettw, 2016/05/24 22:03:31]

According to style I think this should be called pool()/set_pool().

The set_pool call below is a bit weird. Since it's only set once, I think it
might be better just to omit this helper function and have the code in
builder.cc do:
  tool->set_pool(LabelPtrPair<Pool>(record->item()->AsPool()));

[sdefresne, 2016/05/26 15:38:37]

Done.

+  void set_pool_label_pair(const LabelPtrPair<Pool>& pool) { pool_ = pool; }
+
+  void set_pool(const Pool* pool) { pool_.ptr = pool; }
+
   // Other functions ----------------------------------------------------------
 
   // Called when the toolchain is saving this tool, after everything is filled
@@ -191,6 +200,8 @@ class Tool {
     return substitution_bits_;
   }
 
+  bool OnResolved(Err* err);
+
  private:
   SubstitutionPattern command_;
   std::string default_output_extension_;
@@ -209,6 +220,7 @@ class Tool {
   bool restat_;
   SubstitutionPattern rspfile_;
   SubstitutionPattern rspfile_content_;
+  LabelPtrPair<Pool> pool_;
 
   bool complete_;