[turbofan] Move context specialization into JSContextSpecializer.

src/compiler/js-context-specialization.h

Index: src/compiler/js-context-specialization.h
diff --git a/src/compiler/js-context-specialization.h b/src/compiler/js-context-specialization.h
index 1f0c2b817ad3ebcbcf83df508fb6f31414db820c..5804938a53b5f294ac6c2d517ba42b771d7dd1af 100644
--- a/src/compiler/js-context-specialization.h
+++ b/src/compiler/js-context-specialization.h
@@ -18,23 +18,31 @@ class JSOperatorBuilder;
 
 // Specializes a given JSGraph to a given context, potentially constant folding
 // some {LoadContext} nodes or strength reducing some {StoreContext} nodes.
-class JSContextSpecializer : public AdvancedReducer {
+class JSContextSpecializer final : public AdvancedReducer {
  public:
-  JSContextSpecializer(Editor* editor, JSGraph* jsgraph)
-      : AdvancedReducer(editor), jsgraph_(jsgraph) {}
+  JSContextSpecializer(Editor* editor, JSGraph* jsgraph, int context_index,
+                       MaybeHandle<Context> context)
+      : AdvancedReducer(editor),
+        jsgraph_(jsgraph),
+        context_index_(context_index),
+        context_(context) {}
 
-  Reduction Reduce(Node* node) override;
+  Reduction Reduce(Node* node) final;
 
-  // Visible for unit testing.
+ private:
+  Reduction ReduceParameter(Node* node);
   Reduction ReduceJSLoadContext(Node* node);
   Reduction ReduceJSStoreContext(Node* node);
 
- private:
   Isolate* isolate() const;
   JSOperatorBuilder* javascript() const;
   JSGraph* jsgraph() const { return jsgraph_; }
+  int context_index() const { return context_index_; }
+  MaybeHandle<Context> context() const { return context_; }
 
   JSGraph* const jsgraph_;
+  int const context_index_;
+  MaybeHandle<Context> context_;
 
   DISALLOW_COPY_AND_ASSIGN(JSContextSpecializer);
 };