Allocate arguments object on-demand instead of at function entry....

src/ast.cc

Index: src/ast.cc
===================================================================
--- src/ast.cc	(revision 2255)
+++ src/ast.cc	(working copy)
@@ -68,7 +68,7 @@
   // names must be canonicalized for fast equality checks
   ASSERT(name->IsSymbol());
   // at least one access, otherwise no need for a VariableProxy
-  var_uses_.RecordAccess(1);
+  var_uses_.RecordRead(1);
 }