Revert GN declare_args() change.

tools/gn/docs/reference.md

Index: tools/gn/docs/reference.md
diff --git a/tools/gn/docs/reference.md b/tools/gn/docs/reference.md
index ab3233aa4ed5f32d6e2e2bf2388477a6fc5cbea8..1aa56f1d4542e1623bb07afb7f12549834472f46 100644
--- a/tools/gn/docs/reference.md
+++ b/tools/gn/docs/reference.md
@@ -1641,9 +1641,8 @@
 
   The precise behavior of declare args is:
 
-   1. The declare_args() block executes. Any variable defined in the enclosing
-      scope is available for reading, but any variable defined earlier in
-      the current scope is not (since the overrides haven't been applied yet).
+   1. The declare_arg block executes. Any variables in the enclosing scope are
+      available for reading.
 
    2. At the end of executing the block, any variables set within that scope
       are saved globally as build arguments, with their current values being
@@ -1662,10 +1661,12 @@
       like [], "", or -1, and after the declare_args block, call exec_script if
       the value is unset by the user.
 
-    - Because you cannot read the value of a variable defined in the same
-      block, if you need to make the default value of one arg depend
-      on the possibly-overridden value of another, write two separate
-      declare_args() blocks:
+    - Any code inside of the declare_args block will see the default values of
+      previous variables defined in the block rather than the user-overridden
+      value. This can be surprising because you will be used to seeing the
+      overridden value. If you need to make the default value of one arg
+      dependent on the possibly-overridden value of another, write two separate
+      declare_args blocks:
 
         declare_args() {
           enable_foo = true