Update V8 to r6387 as required by WebKit r76408

Change-Id: Icfc5385b0996bd592f8b1ac8cbb44767ee09f1f6
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index a3552c7..f9c57e6 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -670,7 +670,7 @@
 
   int finger = Smi::cast(get(kFingerIndex))->value();
   ASSERT(kEntriesIndex <= finger);
-  ASSERT(finger < size || finger == kEntriesIndex);
+  ASSERT((finger < size) || (finger == kEntriesIndex && finger == size));
   ASSERT_EQ(0, finger % kEntrySize);
 
   if (FLAG_enable_slow_asserts) {