Remember and reuse derived map for external arrays

src/v8globals.h

Index: src/v8globals.h
diff --git a/src/v8globals.h b/src/v8globals.h
index 0933acffdae137cff857ab388fb10e7c9d0c5a95..7ff464af8e878783f050d373df99f172510a9c9f 100644
--- a/src/v8globals.h
+++ b/src/v8globals.h
@@ -318,14 +318,15 @@ enum InlineCacheHolderFlag {
 // Must fit in the BitField PropertyDetails::TypeField.
 // A copy of this is in mirror-debugger.js.
 enum PropertyType {
-  NORMAL              = 0,  // only in slow mode
-  FIELD               = 1,  // only in fast mode
-  CONSTANT_FUNCTION   = 2,  // only in fast mode
-  CALLBACKS           = 3,
-  INTERCEPTOR         = 4,  // only in lookup results, not in descriptors.
-  MAP_TRANSITION      = 5,  // only in fast mode
-  CONSTANT_TRANSITION = 6,  // only in fast mode
-  NULL_DESCRIPTOR     = 7,  // only in fast mode
+  NORMAL                    = 0,  // only in slow mode
+  FIELD                     = 1,  // only in fast mode
+  CONSTANT_FUNCTION         = 2,  // only in fast mode
+  CALLBACKS                 = 3,
+  INTERCEPTOR               = 4,  // only in lookup results, not in descriptors.
+  MAP_TRANSITION            = 5,  // only in fast mode
+  EXTERNAL_ARRAY_TRANSITION = 6,
+  CONSTANT_TRANSITION       = 7,  // only in fast mode
+  NULL_DESCRIPTOR           = 8,  // only in fast mode
   // All properties before MAP_TRANSITION are real.
   FIRST_PHANTOM_PROPERTY_TYPE = MAP_TRANSITION,
   // There are no IC stubs for NULL_DESCRIPTORS. Therefore,