Strawman: check strong mode free variables against the global object.

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index f24f7107d8fd444235349dcc2601166dcc8ebbdc..708de9ac0eb782298959035a0b19c0ad3196be79 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -3668,6 +3668,10 @@ bool CheckAndDeclareArrowParameter(ParserTraits* traits, Expression* expression,
       return false;
     }
 
+    // When the variable was seen, it was recorded as unresolved in the outer
+    // scope. But it's really not unresolved.
+    scope->outer_scope()->RemoveUnresolved(expression->AsVariableProxy());
+
     scope->DeclareParameter(raw_name, VAR);
     ++(*num_params);
     return true;