Move ContextSlotCache to its own file

src/ast/context-slot-cache.h

-// Copyright 2011 the V8 project authors. All rights reserved.
+// Copyright 2016 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_AST_SCOPEINFO_H_
-#define V8_AST_SCOPEINFO_H_
+#ifndef V8_AST_CONTEXT_SLOT_CACHE_H_
+#define V8_AST_CONTEXT_SLOT_CACHE_H_
 
 #include "src/allocation.h"
 #include "src/ast/modules.h"
 #include "src/ast/variables.h"
 
 namespace v8 {
 namespace internal {
 
 // Cache for mapping (data, property name) into context slot index.
 // The cache contains both positive and negative results.
@@ skipping 83 matching lines @@
     uint32_t value_;
   };
 
   Key keys_[kLength];
   uint32_t values_[kLength];
 
   friend class Isolate;
   DISALLOW_COPY_AND_ASSIGN(ContextSlotCache);
 };
 
-
 }  // namespace internal
 }  // namespace v8
 
-#endif  // V8_AST_SCOPEINFO_H_
+#endif  // V8_AST_CONTEXT_SLOT_CACHE_H_