[turbofan]: Add a context relaxation Reducer

src/compiler/js-context-relaxation.h

Index: src/compiler/js-context-relaxation.h
diff --git a/src/compiler/js-context-relaxation.h b/src/compiler/js-context-relaxation.h
new file mode 100644
index 0000000000000000000000000000000000000000..59e06be2c487abab762f9af26110ba23ec285ded
--- /dev/null
+++ b/src/compiler/js-context-relaxation.h
@@ -0,0 +1,40 @@
+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_COMPILER_JS_CONTEXT_RELAXATION_H_
+#define V8_COMPILER_JS_CONTEXT_RELAXATION_H_
+
+#include "src/code-factory.h"
+#include "src/compiler/graph-reducer.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// Ensures that operations that only need to access the native context use the
+// outer-most context rather than the specific context given by the AST graph
+// builder. This makes it possible to use they operations with context
+// specialization (e.g. for generating stubs) without forcing inner contexts to
+// be embedded in generated code thus causing leaks.
+class JSContextRelaxation final : public Reducer {
+ public:
+  JSContextRelaxation(Node* start, Node* relaxed_context)
+      : start_(start),
+        relaxed_context_(relaxed_context),
+        context_is_wired_(false) {}
+  ~JSContextRelaxation() final{};
+
+  Reduction Reduce(Node* node) final;
+
+ private:
+  Node* start_;
+  Node* relaxed_context_;
+  bool context_is_wired_;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_JS_CONTEXT_RELAXATION_H_