Add support for reading .gypi files.

tools/gn/parse_tree.cc

Index: tools/gn/parse_tree.cc
diff --git a/tools/gn/parse_tree.cc b/tools/gn/parse_tree.cc
index 4015fd1f353149acfd0d610b5f7eddc3cf52c608..f93b53854d55944507015a037bb6c7e95dcd4074 100644
--- a/tools/gn/parse_tree.cc
+++ b/tools/gn/parse_tree.cc
@@ -53,10 +53,25 @@ const AccessorNode* AccessorNode::AsAccessor() const {
 }
 
 Value AccessorNode::Execute(Scope* scope, Err* err) const {
-  if (index_)
+  if (index_) {
     return ExecuteArrayAccess(scope, err);
-  else if (member_)
-    return ExecuteScopeAccess(scope, err);
+  } else if (member_) {
+    const Value* value = scope->GetValue(base_.value(), true);
+    if (!value) {
+      *err = MakeErrorDescribing("Undefined identifier.");
+      return Value();
+    }
+    if (value->type() == Value::SCOPE) {
+      return ExecuteScopeAccess(scope, err);
+    } else if (value->type() == Value::DICT) {
+      return ExecuteDictAccess(value, err);
+    } else {
+      *err = MakeErrorDescribing(
+          std::string("Type \"") + Value::DescribeType(value->type()) +
+          "\" is not usable with the '.' operator.");
+      return Value();
+    }
+  }
   NOTREACHED();
   return Value();
 }
@@ -165,6 +180,17 @@ Value AccessorNode::ExecuteScopeAccess(Scope* scope, Err* err) const {
   return *result;
 }
 
+Value AccessorNode::ExecuteDictAccess(const Value* dict, Err* err) const {
+  std::map<std::string, Value>::const_iterator found =
+      dict->dict_value().find(member_->value().value().as_string());
+  if (found == dict->dict_value().end()) {
+    *err = Err(member_.get(), "No value named \"" +
+        member_->value().value() + "\" in scope \"" + base_.value() + "\"");
+    return Value();
+  }
+  return found->second;
+}
+
 // BinaryOpNode ---------------------------------------------------------------
 
 BinaryOpNode::BinaryOpNode() {