Make non-Module generators only context allocate parameters.

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index d2f9c74e58b3246e2228d17b1c6c4ee47a59541f..ff409bd8e14aac8d649e19fb20a665d719eec95e 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -706,6 +706,7 @@ FunctionLiteral* Parser::DoParseProgram(ParseInfo* info) {
       var->AllocateTo(VariableLocation::PARAMETER, 0);
 
       PrepareGeneratorVariables();
+      scope->ForceContextAllocation();
       Expression* initial_yield =
           BuildInitialYield(kNoSourcePosition, kGeneratorFunction);
       body->Add(
@@ -2536,7 +2537,7 @@ void Parser::PrepareGeneratorVariables() {
   // it minimizes the work needed to suspend and resume an activation.  The

[adamk, 2017/05/23 20:20:38]

This first sentence is now obsolete, and should be removed; I think the rest of
the comment stands on its own.

[Jarin, 2017/05/24 05:03:27]

Done.

   // code produced for generators relies on this forced context allocation (it
   // does not restore the frame's parameters upon resume).
-  function_state_->scope()->ForceContextAllocation();
+  function_state_->scope()->ForceContextAllocationForParameters();
 
   // Calling a generator returns a generator object.  That object is stored
   // in a temporary variable, a definition that is used by "yield"