[generators] Add some explanation on forcing context allocation.

src/full-codegen/arm64/full-codegen-arm64.cc

Index: src/full-codegen/arm64/full-codegen-arm64.cc
diff --git a/src/full-codegen/arm64/full-codegen-arm64.cc b/src/full-codegen/arm64/full-codegen-arm64.cc
index 1c38a44a3cd7bb8538ca5be467ac5733a54a7cb1..2a022e5c676c680cc9d6d5e6fcb5d940a4fe0281 100644
--- a/src/full-codegen/arm64/full-codegen-arm64.cc
+++ b/src/full-codegen/arm64/full-codegen-arm64.cc
@@ -3844,7 +3844,10 @@ void FullCodeGenerator::EmitGeneratorResume(Expression *generator,
                               JSGeneratorObject::kReceiverOffset));
   __ Push(x10);
 
-  // Push holes for the rest of the arguments to the generator function.
+  // Push holes for arguments to generator function. Since the parser forced
+  // context allocation for any variables in generators, the actual argument
+  // values have already been copied into the context and these dummy values
+  // will never be used.
   __ Ldr(x10, FieldMemOperand(function, JSFunction::kSharedFunctionInfoOffset));
 
   // The number of arguments is stored as an int32_t, and -1 is a marker