Update comments on context slots.

src/contexts.h

 // Copyright 2012 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_CONTEXTS_H_
 #define V8_CONTEXTS_H_
 
 #include "src/heap/heap.h"
 #include "src/objects.h"
 
@@ skipping 315 matching lines @@
 //
 // [ closure   ]  This is the current function. It is the same for all
 //                contexts inside a function. It provides access to the
 //                incoming context (i.e., the outer context, which may
 //                or may not become the current function's context), and
 //                it provides access to the functions code and thus it's
 //                scope information, which in turn contains the names of
 //                statically allocated context slots. The names are needed
 //                for dynamic lookups in the presence of 'with' or 'eval'.
 //
-// [ previous  ]  A pointer to the previous context. It is NULL for
-//                function contexts, and non-NULL for 'with' contexts.
-//                Used to implement the 'with' statement.
+// [ previous  ]  A pointer to the previous context.
 //
 // [ extension ]  A pointer to an extension JSObject, or "the hole". Used to
 //                implement 'with' statements and dynamic declarations
 //                (through 'eval'). The object in a 'with' statement is
 //                stored in the extension slot of a 'with' context.
 //                Dynamically declared variables/functions are also added
 //                to lazily allocated extension object. Context::Lookup
 //                searches the extension object for properties.
 //                For script and block contexts, contains the respective
 //                ScopeInfo. For block contexts representing sloppy declaration
 //                block scopes, it may also be a struct being a
 //                SloppyBlockWithEvalContextExtension, pairing the ScopeInfo
 //                with an extension object.
 //
-// [ global_object ]  A pointer to the global object. Provided for quick
-//                access to the global object from inside the code (since
-//                we always have a context pointer).
+// [ native_context ]  A pointer to the native context.
 //
 // In addition, function contexts may have statically allocated context slots
 // to store local variables/functions that are accessed from inner functions
 // (via static context addresses) or through 'eval' (dynamic context lookups).
 // The native context contains additional slots for fast access to native
 // properties.
 //
 // Finally, with Harmony scoping, the JSFunction representing a top level
 // script will have the ScriptContext rather than a FunctionContext.
 // Script contexts from all top-level scripts are gathered in
@@ skipping 206 matching lines @@
 #endif
 
   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CONTEXTS_H_