Allow creation and modification of scopes in GN.

tools/gn/parser.h

Index: tools/gn/parser.h
diff --git a/tools/gn/parser.h b/tools/gn/parser.h
index de828a4ecdffddf78616b4331b489a8a3a648842..29580da2b4a2946341c760ba2b43e01ae7c2f4af 100644
--- a/tools/gn/parser.h
+++ b/tools/gn/parser.h
@@ -58,6 +58,7 @@ class Parser {
   std::unique_ptr<ParseNode> ParseExpression(int precedence);
 
   // |PrefixFunc|s used in parsing expressions.
+  std::unique_ptr<ParseNode> Block(Token token);
   std::unique_ptr<ParseNode> Literal(Token token);
   std::unique_ptr<ParseNode> Name(Token token);
   std::unique_ptr<ParseNode> Group(Token token);
@@ -85,7 +86,10 @@ class Parser {
 
   std::unique_ptr<ParseNode> ParseFile();
   std::unique_ptr<ParseNode> ParseStatement();
-  std::unique_ptr<BlockNode> ParseBlock();
+  // Expects to be passed the token corresponding to the '{' and that the
+  // current token is the one following the '{'.
+  std::unique_ptr<BlockNode> ParseBlock(Token being_brace,
+                                        BlockNode::ResultMode result_mode);
   std::unique_ptr<ParseNode> ParseCondition();
 
   // Generates a pre- and post-order traversal of the tree.