Remove the fcontext field from all contexts.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 0ce5e34aa0bebf566ff0e83feb33cda54efbfd7e..607eda7ebdd0218ca0df2ff021fcf794997a3f3a 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -3932,7 +3932,6 @@ MaybeObject* Heap::AllocateFunctionContext(int length, JSFunction* function) {
   Context* context = reinterpret_cast<Context*>(result);
   context->set_map(function_context_map());
   context->set_closure(function);
-  context->set_fcontext(context);
   context->set_previous(function->context());
   context->set_extension(NULL);
   context->set_global(function->context()->global());
@@ -3952,7 +3951,6 @@ MaybeObject* Heap::AllocateCatchContext(Context* previous,
   Context* context = reinterpret_cast<Context*>(result);
   context->set_map(catch_context_map());
   context->set_closure(previous->closure());
-  context->set_fcontext(previous->fcontext());
   context->set_previous(previous);
   context->set_extension(name);
   context->set_global(previous->global());
@@ -3970,7 +3968,6 @@ MaybeObject* Heap::AllocateWithContext(Context* previous,
   Context* context = reinterpret_cast<Context*>(result);
   context->set_map(with_context_map());
   context->set_closure(previous->closure());
-  context->set_fcontext(previous->fcontext());
   context->set_previous(previous);
   context->set_extension(extension);
   context->set_global(previous->global());