Update V8 to r5091 as required by WebKit r63859.

Change-Id: I8e35d765e6f6c7f89eccff900e1cabe2d5dd6110
diff --git a/src/full-codegen.cc b/src/full-codegen.cc
index b64a179..8a8b39b 100644
--- a/src/full-codegen.cc
+++ b/src/full-codegen.cc
@@ -857,6 +857,8 @@
     EmitIsNonNegativeSmi(expr->arguments());
   } else if (strcmp("_IsObject", *name->ToCString()) == 0) {
     EmitIsObject(expr->arguments());
+  } else if (strcmp("_IsSpecObject", *name->ToCString()) == 0) {
+    EmitIsSpecObject(expr->arguments());
   } else if (strcmp("_IsUndetectableObject", *name->ToCString()) == 0) {
     EmitIsUndetectableObject(expr->arguments());
   } else if (strcmp("_IsFunction", *name->ToCString()) == 0) {