Heavy cleanup of the external pointer API.

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 28e4af53682b2fa6a55623914720d7939bbd0285..53a7c2d460b46b74532b41c14acda1af647b9365 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -152,7 +152,7 @@ enum BindingFlags {
   V(CONTEXT_EXTENSION_FUNCTION_INDEX, JSFunction, context_extension_function) \
   V(OUT_OF_MEMORY_INDEX, Object, out_of_memory) \
   V(MAP_CACHE_INDEX, Object, map_cache) \
-  V(CONTEXT_DATA_INDEX, Object, data) \
+  V(EMBEDDER_DATA_INDEX, FixedArray, embedder_data) \
   V(ALLOW_CODE_GEN_FROM_STRINGS_INDEX, Object, allow_code_gen_from_strings) \
   V(ERROR_MESSAGE_FOR_CODE_GEN_FROM_STRINGS_INDEX, Object, \
     error_message_for_code_gen_from_strings) \
@@ -281,7 +281,7 @@ class Context: public FixedArray {
     OPAQUE_REFERENCE_FUNCTION_INDEX,
     CONTEXT_EXTENSION_FUNCTION_INDEX,
     OUT_OF_MEMORY_INDEX,
-    CONTEXT_DATA_INDEX,
+    EMBEDDER_DATA_INDEX,
     ALLOW_CODE_GEN_FROM_STRINGS_INDEX,
     ERROR_MESSAGE_FOR_CODE_GEN_FROM_STRINGS_INDEX,
     TO_COMPLETE_PROPERTY_DESCRIPTOR_INDEX,
@@ -446,6 +446,9 @@ class Context: public FixedArray {
   static bool IsBootstrappingOrValidParentContext(Object* object, Context* kid);
   static bool IsBootstrappingOrGlobalObject(Object* object);
 #endif
+
+  STATIC_CHECK(kHeaderSize == Internals::kContextHeaderSize);
+  STATIC_CHECK(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 };
 
 } }  // namespace v8::internal