[Turbofan] BytecodeGraphBuilder: Use native context directly.

In BuildLoadNativeContextField(), we have access to the native context
as a constant. Use it directly, rather than loading from the current
context.

Change-Id: I60cd97586bbe5f8336f809967a3df556d0d43049
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1630682Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61871}

src/compiler/bytecode-graph-builder.cc

@@ -996,11 +996,9 @@ Node* BytecodeGraphBuilder::GetFunctionClosure() {
 }
 
 Node* BytecodeGraphBuilder::BuildLoadNativeContextField(int index) {
-  const Operator* op =
-      javascript()->LoadContext(0, Context::NATIVE_CONTEXT_INDEX, true);
-  Node* native_context = NewNode(op);
   Node* result = NewNode(javascript()->LoadContext(0, index, true));
-  NodeProperties::ReplaceContextInput(result, native_context);
+  NodeProperties::ReplaceContextInput(
+      result, jsgraph()->HeapConstant(native_context()));
   return result;
 }