Add support for user defined "pool" to GN.

tools/gn/builder.cc

Index: tools/gn/builder.cc
diff --git a/tools/gn/builder.cc b/tools/gn/builder.cc
index 22b4c478c9bd347ded71d84ad6b14469df99cf22..318931e4a46a9cee68e8a1779d708b63a0cf1c14 100644
--- a/tools/gn/builder.cc
+++ b/tools/gn/builder.cc
@@ -263,6 +263,20 @@ bool Builder::ToolchainDefined(BuilderRecord* record, Err* err) {
   if (!AddDeps(record, toolchain->deps(), err))
     return false;
 
+  for (int i = Toolchain::TYPE_NONE + 1; i < Toolchain::TYPE_NUMTYPES; i++) {
+    Toolchain::ToolType tool_type = static_cast<Toolchain::ToolType>(i);
+    Tool* tool = toolchain->GetTool(tool_type);
+    if (!tool || tool->pool_label_pair().label.is_null())
+      continue;
+
+    BuilderRecord* dep_record = GetOrCreateRecordOfType(
+        tool->pool_label_pair().label, tool->pool_label_pair().origin,
+        BuilderRecord::ITEM_POOL, err);
+    if (!dep_record)
+      return false;
+    record->AddDep(dep_record);
+  }
+
   // The default toolchain gets generated by default. Also propogate the
   // generate flag if it depends on items in a non-default toolchain.
   if (record->should_generate() ||
@@ -429,6 +443,8 @@ bool Builder::ResolveItem(BuilderRecord* record, Err* err) {
     Toolchain* toolchain = record->item()->AsToolchain();
     if (!ResolveDeps(&toolchain->deps(), err))
       return false;
+    if (!ResolvePools(toolchain, err))
+      return false;
   }
 
   record->set_resolved(true);
@@ -497,6 +513,30 @@ bool Builder::ResolveToolchain(Target* target, Err* err) {
   return true;
 }
 
+bool Builder::ResolvePools(Toolchain* toolchain, Err* err) {
+  for (int i = Toolchain::TYPE_NONE + 1; i < Toolchain::TYPE_NUMTYPES; i++) {
+    Toolchain::ToolType tool_type = static_cast<Toolchain::ToolType>(i);
+    Tool* tool = toolchain->GetTool(tool_type);
+    if (!tool || tool->pool_label_pair().label.is_null())
+      continue;
+
+    BuilderRecord* record = GetResolvedRecordOfType(
+        tool->pool_label_pair().label, toolchain->defined_from(),
+        BuilderRecord::ITEM_POOL, err);
+    if (!record) {
+      * err = Err(tool->pool_label_pair().origin,
+          "Pool for tool not defined.",
+          "I was hoping to find a pool " +
+          tool->pool_label_pair().label.GetUserVisibleName(false));
+      return false;
+    }
+
+    tool->set_pool(record->item()->AsPool());
+  }
+
+  return true;
+}
+
 std::string Builder::CheckForCircularDependencies(
     const std::vector<const BuilderRecord*>& bad_records) const {
   std::vector<const BuilderRecord*> cycle;