Allow dependencies of toolchains in GN.

tools/gn/builder.cc

Index: tools/gn/builder.cc
diff --git a/tools/gn/builder.cc b/tools/gn/builder.cc
index 132f4e0a604df5b6a023056cd9be3a2d4526ba13..50a027b389de3352afe54e67329c9ed2310a980e 100644
--- a/tools/gn/builder.cc
+++ b/tools/gn/builder.cc
@@ -91,17 +91,18 @@ void Builder::ItemDefined(scoped_ptr<Item> item) {
   // loads for targets that are required.
   switch (type) {
     case BuilderRecord::ITEM_TARGET:
-      if (!TargetDefined(record, &err)) {
-        g_scheduler->FailWithError(err);
-        return;
-      }
+      TargetDefined(record, &err);
       break;
     case BuilderRecord::ITEM_TOOLCHAIN:
-      loader_->ToolchainLoaded(record->item()->AsToolchain());
+      ToolchainDefined(record, &err);
       break;
     default:
       break;
   }
+  if (err.has_error()) {
+    g_scheduler->FailWithError(err);
+    return;
+  }
 
   if (record->can_resolve()) {
     if (!ResolveItem(record, &err)) {
@@ -243,6 +244,22 @@ bool Builder::TargetDefined(BuilderRecord* record, Err* err) {
   return true;
 }
 
+bool Builder::ToolchainDefined(BuilderRecord* record, Err* err) {
+  Toolchain* toolchain = record->item()->AsToolchain();
+
+  if (!AddDeps(record, toolchain->deps(), err))
+    return false;
+
+  // 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() ||
+      toolchain->settings()->default_toolchain_label() == toolchain->label())
+    RecursiveSetShouldGenerate(record, true);
+
+  loader_->ToolchainLoaded(toolchain);
+  return true;
+}
+
 BuilderRecord* Builder::GetOrCreateRecordOfType(const Label& label,
                                                 const ParseNode* request_from,
                                                 BuilderRecord::ItemType type,
@@ -380,6 +397,10 @@ bool Builder::ResolveItem(BuilderRecord* record, Err* err) {
         !ResolveConfigs(&target->direct_dependent_configs(), err) ||
         !ResolveForwardDependentConfigs(target, err))
       return false;
+  } else if (record->type() == BuilderRecord::ITEM_TOOLCHAIN) {
+    Toolchain* toolchain = record->item()->AsToolchain();
+    if (!ResolveDeps(&toolchain->deps(), err))
+      return false;
   }
 
   record->set_resolved(true);